Oh man i'm not sure about this one i mean the whole PLR market is in the grey area but since it's PLR + i'm sure there's not a
SINGLE seller who've purchased and has a license from every single author
I'm sure you won't get hurt
Since i can't give legal advice and didn't put this type of business on a large scale into action i'm not sure
One thing is for sure man i've never heard of any legal cases in the market in general (Canva templates, PLR, PD/CC etc.)
If you have any doubts (and that's great for your own safety) you can buy a pack from websites like the one you've mentioned above and resell them
The thing is, what if the nicely branded website is just a guy with basic HTML/CSS skills reselling a few PLR packs he doesn't have any official license to them?
You'll never know.
This brings us to point A. PLR ebooks are
RESELLABLE 
You'll get the unmodified books (even if they've been modified, you can still edit them but i'm confident they just resell the original copies)
So once your hands are on a PLR pack, you can do as you wish
I'm not here to get you into any potential trouble. This market gave me the impression or a 'resell based' business since day one. And since it's PLR/MRR or whatever the case may be we're taking, i think you're good
I've also haven't seen an original author selling his content besides these so called "databases" and i've also ran these books on plagiarism checkers plenty of times and i've seen them on plenty of blogs as well (I was doing the same thing back in 2017 but i was spinning them)
Better check the topic deeper and ask for any crucial information on the legal side of things but basically, that's free resellable information and what they're doing is obviously, reselling