Are there specific features to look for? Brands to avoid? Is FRS even the right thing?
Some more information would be needed to really answer your question well.
FRS and GMRS both use UHF frequencies that work primarily by line of sight. In other words, if the two antennas can "see" each other, than likely they can talk.
More power, as in going from the old 0.5 watt FRS radios to the newer 2 watt radios will not equal a 4x increase in range. It'll just slightly improve the readability when you get out on the fringes. Line of sight is still line of sight.
Describing the environment(s) they are used in would help. Also, a description of the topography of the area would help. Is it flat, hills, buildings, how far do you need to communicate?
Usually the common issue with any low tier consumer radio has to do with two thing:
Poor antenna (but hey, at leas the
look cool, right?)
Poor receiver
Often the low end radios have receivers that are not very sensitive, so they tend to do poorly when surrounded by appliances and consumer electronics that make a lot of RF noise.
Without knowing all the details, it's hard to make a recommendation, but you might be better served by one of the following:
Check into MURS, Multi Use Radio Service. It's made up of 5 channels in the VHF spectrum and permits running 2 watts (like most FRS channels). The difference is that you can use replaceable antennas (FRS cannot by FCC rule). The radios cost more, but they might be a good investment. Ritron makes a nice model, my brother in law uses them for his tower crews:
https://www.ritron.com/PTSeries-Ritron-2-Way-Radios He's using the PT-150M
They also make a few other models, including some desktop bases that will run off 110vac power:
https://www.ritron.com/2-way-radios
VHF/MURS does a bit better in terrain where UHF might not work well.
The other thing you might want to consider, if this is a short term camp, or "summer" only, is renting some radios for a local radio shop. Again, it'll cost more, but then you don't have to worry too much about the radios. Rent them when needed, send them back when not. The shop takes care of maintenance, batteries, etc.
Another option -might- be some of the Motorola DTR series 900MHz radios. Again, more expensive than the consumer grade FRS/GMRS radios, but can work a bit better in some cases. Same line of sight issues apply, so test them first before buying a bunch.
Steer clear of the low tier Chinese radios. Any brand name you cannot pronounce, or that you buy in bulk off e-Bay or Amazon is a real bad idea. Many of them do not have FCC type certifications and would not be legal to use anywhere other than the amateur radio bands. They have little or no filtering on their receivers, so they can have issues in high RF noise environments. While cheap, you can and should do better.
Fill us in on some of the details (the more details, the better) and it would make it easier to make a recommendation.