I admire your forethought and planning and appreciate that you shared with us!
The provisions you listed were per person, right? Haha!
Your issues with the mobile phones is interesting and in retrospect, not a surprise. That makes a strong case for having a few FMRS or GMRS radios among your groups for short range communications.
F*** FRS. Get GMRS, full 5W. FRS .5w are worthless beyond line of sight. Even "reasonably" priced GMRS may not be the full 5w as allowed by the FCC. I had a set I tried on vacation. I could get about 1.25 mile out of them 5x5. But at 1.25+ 500' with a 6' elevation drop behind an earthen wall it was lights out. Switching to a MURS radio that was known absolutely to be 4w it was no problem whatsoever. I was back to 5x5.
The problem is the retail FRS/GMRS producers are refusing to advertise the actual output power. They instead hide behind obscure distance ratings that dont mean squat. Yes, pure power is not the end all for distance, but it is a good 60-80% indicator of performance.
If you want GMRS radios that dont hide behind distance ratings and advertise the actual output, try these. Still not sure how they fit the requirements since they dont appear to have fixed antennae... (I have not tried them, but do use their other products as a HAM)
https://baofengtech.com/gmrs-v1
These also have good ratings that seem to jive with the distance of a 5w GMRS. But once again, you wont find wattage ratings ANYWHERE on these, so buyer beware.
https://www.amazon.com/dp/B001WMFYH4/_encoding=UTF8?coliid=I16T76KSAUZGMG&colid=3U41SQX8Y5V3T