Lisa, my experience is that, when we are camping, we can make an average cellphone used for a Dexcom last more than 2.5 days, that’s less than 1,250 mAh per day. For that we turn off a lot of functionality on the cellphone, such as location services, cellular service, wifi etc. I am pretty sure that any of the chargers we discussed can charge more than 1,200 mAh per day on average. So, if you take a 15,000 mAh battery with a small combined solar charger for each cellphone, I think you are really well protected.
As a comparison, my son and I were kayak camping for over a week recently. He was using a 1-year-old iPhone SE, and would use up a 3,000 mAh power bank about every 2.5 days.
If you were to use the location services in your cellphone (GPS), or browse the net (or stream) you would use a lot more battery. But, for us, when we go camping untethered we don’t do any of that. So, if that is the same for you, my vote is for nothing smaller than 15,000 mAh, with a 5"x3" (approx) solar panel. That should keep you safe in almost any weather, between the ability to charge some and the large battery reserve.
Be aware, however, that, if you need 1,250 real mAh per day, you actually lose more than that from your battery because there are losses. I would guess that if you use 1,250 mAh/day in your phone you are probably using 1,750 mAh of battery reserve.
Since I like to have redundancy, I would take one per phone and add one more for a spare. I don’t think you need the larger, folder type of solar panel (I would consider it if you went for more than a week at a time).