The reason why people using a lot of accounts use proxies is that they don't want Instagram to know that they have X amounts of account and that those accounts are part of a network. It's to avoid to leave a footprint.
It's pretty much the same thing as when you build a PBN for SEO purpose. You don't want Google to be able to realize that you are manipulating your algorithm by building your own network so you put each blog on different host to avoid to leave a footprint that would allow them to connect the dots and have proof that you own them all.
Instagram allow someone to manage up to 5 accounts. Above that it looks suspicious to their eyes.
If you're just botting two accounts you should be fine with leaving the account on the same proxy. However if you plan to expand your network it could start to be tricky as instagram pretty much already know that those two accounts are "interlinked" as they were probably created on the same ip address and they run on the same IP address atm.
Whenever you're wondering if something is going to hurt your grow on IG think of it this way and ask yourself this question. "Will doing what I have in mind give Instagram more clues that I am running a network of IG accounts/IG farm or whatever you want to call it?"
If you don't run an IG farm and you have less than 5 accounts you'll be fine.
If you run an IG farm and the answer is that it will give them more clues, don't do it.
If you run an IG farm and the answer is that it will NOT give them more clues, you'll be find.
It's all about common sense and understanding why you use something.
I know I went a little overboard with this answer but I hope it helped you understand the process.