re: "They don't want 5G".....you know todays wifi is in the 5 GHz spectrum? The "tin foil hats" that are afraid of "5G" connectivity are referring to the cellular 5G that is coming out, not the 5 gig wifi.
For outdoors, you really want the real "outdoor" APs....so you have the UAP-M...and the UAP-M-Pro
UAP-M is the little inexpensive one with a pair of little rabbit ear antennas. Can handle a light to almost moderate load. The Pro version is the higher priced big rectangular one...can handle a pretty good load. There is also a big expensive model meant for mega-huge loads like stadiums...but we'll leave that out of this one.
As for 900mHz vs 2.4 vs 5 for the point to point airmax radios....and the trees. Short distance....I've seen 5 go through some trees pretty good. Trimming them can do wonders....just have to "punch a hole" through the limbs to give the fresnel zone a path. Also...the type of tree can have an impact. Deciduous trees for the most part have the least obstruction....versus, pine/conifer type trees...which block more. Deciduous trees can slow things down after heavy rain...as the leaves are filled with water more. But if you just trim a few limbs down to clear a line of site path through, about a 25' hole....or at least clear as much as you can, it can do wonders. I've had bucket trucks do a lot of tree trimming!
Have an indoor AP on the inside of buildings, and an outdoor AP on the outside. Outdoor APs...stand them off of (away from) walls as best you can, you can get some good mounting brackets to do that. If you mount them right onto walls...performance isn't as good as if they were a foot away from a wall. Also down a bit from overhangs. Ideally, not more than 14' AGL (above ground level). Mount APs too high, and the signal just shoots over peoples who are on the grounds heads. For point to point radios...you can mount as high as you want (higher is better)..they just need to see each other well, and you're not blanketing wifi with them.