Hi there! We're RVers here, and I love to see more families doing it, because it can be very educational and lots of fun
What type of RV are you renting? I assume a Class A or Class C (the kind you drive vs the kind you pull), since those are the most commonly available type for rent.
As the previous poster said, you have to be careful about seatbelt situations in those. The two front seats will have seatbelts. There will likely be other seatbelts, too, but maybe not good/usable ones. Sometimes they're attached to the frame, but sometimes they're just attached to the plywood floor.
Sometimes they're on side-facing couches. Unfortunately, those can't be used to install car seats (car seats aren't allowed to be installed on side-facing seats). They're also usually lap-only, which isn't safe for anything other than installing a car seat, but again, you can't do that.
Plus there are projectile risks, as mentioned. In a crash, anything in the RV--even things in cabinets...or even the cabinets themselves--become potential projectiles.
What I would recommend is that you look into renting a travel trailer or fifth wheel. If you don't have a vehicle that can tow it, borrow one from someone you know, or rent one of those, too. (Regular rental car places usually won't rent for towing, but there are places that will.)
If that absolutely isn't an option, my second preference would be that one person drives the motorhome and the other drives the regular car with the kids inside. That also gives you the benefit of having a car at your destination, without having to unhook/tow anything.
If that's not an option, and you are going to rent and have everyone travel in the motorhome, all I can recommend is that you do your best. Scope out the seatbelt locations. If they're at a dinette, remove the dinette table. I wouldn't want my kids slamming into that. Then secure the table somewhere, like in the underbelly storage. Make sure all cabinets and doors are closed and everything is stowed, like on an airplane.. NO GETTING UP FOR DRINKS/POTTY/PLAYTIME EVER while the vehicle is in motion. Pull over for that.
I don't think Class A and C typically have airbags, so if you needed/wanted to put a kid up front, that would possibly be an option.
As for the installation itself, your seats should install the same way they do in your car, although an RV is unlikely to have LATCH, just seatbelts. If you're not used to installing your seats with the belt, it's usually pretty easy.