Compared to pretty much everybody here the way I think about this is much, much more complex and at the same time more simple. Increase of complexity in one area simplifies the understanding in other ares. I'm not saying this to brag but I find it a bit amazing and interesting the way you all think and the fact it is so similar. You may disagree with each other, mainly being split in a few camps (yes/no, evolutionism/creationism, good/evil, aliens/god, etc) but the fact is, you fit in a thinking category and have a certain rationale. When I realized this I realized it comes from people being able to process and interpret information only in a certain way, based on their concepts, knowledge, past experiences, etc. This is not a novelty, has been thought of and talked about by others since a long time ago.
First thing you need to realize about yourself is the way you think about this (and anything for that matter) sprouts from the information you were fed. I don't mean that necessarily in a conspiracy/brainwashing way, though that's a reality too. Thing is YOU didn't actually came to these conclusions yourself but instead you were given throughout your life, variants in which to believe and from which to pick. You did not actually thought of it from zero, you were seeded with information.
Another aspect is your capacity to handle information, make sense of it and use it when doing reflection, deduction and all the logic processes. Simply put, a piece of information is understood by a person his own way not the way it was transmitted. If you read a book, you understand it your own way, subjectively not objectively. In fact there is no such think as objectivity. Objectivity is just the majority of people agreeing on something in a totaly subjective way that is however similar among each other. Also, most of the time (hopefully) objectivity involves a very strict reference frame. In other words we all agree that a person that is 2.30 meter tall is a very tall person. The reference frame here is "human person". If you talk about anything, then the statement stops being valid. A law of physics also stands correct and valid only within a certain reference frame - the perceivable universe - because physical laws are deducted from observation of this universe not another universe nor of an "expanded" version achieved for example through some kind of sensory enhancement/expansion/adaptation (and by sensory i include not just human senses but measurement/conversion devices that us humans have developed - because they allow an extension of our natural senses).
To answer the question about aliens you must first define what an alien is. Same with God or with anything. Then you need to get in the position where you observe (sense) an alien or God or whatever thing you are curious if it exists. Logically speaking, the only way to proof that something exists or doesn't exist is if it actually exists and you discover it. Otherwise it is undetermined, which is not synonym with "does not exist". Interestingly enough from a logical way it is impossible for something to not exist

You may deduct through certain observations that certain things are incompatible (always within a certain reference frame), hence say X does not exist because Y exists. So you say a red tomato is red but not pure white or some other color. Because that is how YOU observe it. This is totally valid in your reference frame. It is not valid in the reference frame of a blind person or an animal that has no sense to detect red. You may say that red is a certain wavelength, hence fixed, hence objective regardless if the observer perceives that wavelength or not. But that's not what red is. Red is a human concept about a humanly observable effect. The tomato is NOT red. How something is or isn't, all meaning as a matter of fact, is completely a subjective and mental thing. You give meaning to things! Something is not in a certain way, YOU think it is in a certain way.
Now let's assume we define an alien as being a biological being from outer space. We have set a reference frame. This way we chose to ignore most of the potential beings out there because now we're only interested in a biological being. If we want it to be intelligent we limit things even further, especially since it must be intelligent in a way similar to human intelligent. A being that is not intelligent in a way comparable to a normal human does not count. A being that is beyond human intelligence does not count. A being that has identical intelligence but in a different way, does not count. What I mean by this last statement? A being might be "identically" intelligent as a regular human in a quantitative way but not in implementation/technical aspect of intelligence. So the being might be able to handle everything we can handle and nothing more but by having completely different thinking, meanings, etc. This is rather abstract but I hope you get it. In other words we might sit in front of each other and be similarly intelligent but because we're not intelligent in the same way, we won't even be able to see each other. But let's go back to the biological, intelligent (in a human compatible way) aliens.
Since we have a reference frame, we now know things about these aliens. For example they are obviously material - biological implies material - and they can communicate - because they must have compatible intelligence (hence abilities) with us. There are thing which we might be tempted to assume and take as facts though they are not true (fallacies). We might assume they travel using spacecrafts. That might not be true however. We use spacecrafts (of a certain kind) but it doesn't mean they do. Same way Amish people use carts not cars and natives in the Amazonian forest use boats that have no engine but paddles (because they don't know what an engine is). And yes natives from Amazon are technically just as intelligent as somebody from NYC (IQ is more or less within same range regardless of environment).
Then there's the question if we're ok with aliens like these that are not technologically or knowledge-wise superior to us, hence can't travel across galaxies, or we want aliens that are superior in this area and can reach us. Because they might be compatible with us, but at the same time be inferior or superior in these areas.
And this thing goes on and on where we must set boundaries and rules about what an alien is and isn't. I'll stop here though. Thing is, I just wanted to point out some of the logic I use when I think about things. Is a lot more to it but this thread would end up humongous if I keep going.
About the incompatibility between aliens and religions, holy books, etc.
I think reading a book literally doesn't take you far. Even less so with holy books. Let's assume the information in them is 100% accurate - the source information was 100% accurate. This simplifies things. So we have certain writings that say something 100% accurate however, if we do not understand that information the way it was meant, we do not get 100% accurate meaning. And that's where the problem lies because there are many ways to think of something and to read something in the absence of the writer to tell you exactly what he meant. Add to that multiple translations, removal of information (e.g. apocryphal gospels), introduction of information, alterations, different cultural and social status from the writer, difference in time frame, etc. and you realize is not that easy to understand holy books especially if you take things literally.
Some here say there's an incompatibility because the Bible states God created the man in his image. Assuming that is true, are you sure "man" means human from Terra? Maybe it means "biological being", "human-type being on any planet" (who said we are the only humans in the universe?), "spirit the man has inside", "potential to become God" (we are evolving, so are we sure "created" is about an act in past completed 100% and not a potential?) or a lot of other things that it could me but I won't go into because you'd probably loose me.
So maybe the incompatibilities you see between the idea of aliens and God or holy writings is not because an incompatibility exists but because that is how YOU understand things. Because the way you understand God, religion, holy teachings or aliens, being subjective, produces this incompatibility. I'm not saying something exists or not or that the holy books are 100% accurate or not or that religion is spot on or not. What I am saying is
understanding things requires you not to limit yourself in existing narrow frames of reference, mentalities, dogmas and perceptions but to allow yourself to truly think free. Not create incompatibilities but accept all possibilities as valid even though they are apparently opposing and incompatible. Then, when you actually get to understand something maybe you will be in a position where there is no more duality - good/bad, true/false, valid/invalid, etc. - but they all exist at once because you transcended that need for binary logic.
I'm not saying I'm a genius who figured shit out because I haven't. That's simply how I think of things and the approach I try to take.
I hope this helped somebody.