They live in hights, because the grounds are too dangerous
This indicates that all is not quite as peaceful as the rest of your comment seemed to indicate. I'm presuming there are some pretty nasty predators at ground-level if the entirety of human civilization in the area doesn't even attempt to touch the forest floor. Also war might be rare as we know it, but tribal raiding in hunter-gather societies almost certainly took a higher death toll (percentage wise) than modern industrial warfare, and it didn't stop just because food and shelter was plentiful. (For details I suggest the excellent "War Before Civilization" by Lawrence Keeley.
So you have two threats that cannot be overcome with your current setup of large branches to shelter from rain and storm. SOME form of man-made shelter would be necessary. Because I'm a nerd we'll refer to this structure as a "Flet". Probably your people would set up around some of these arboreal wells you mentioned, as a reliable water source is always handy. Next, they would "fortify" the flet. I'm going to make an assumption that your forest, like all forests, have vines that climb trees and potentially exploit them for nutrients. Poison Ivy is one such vine common in north america, and can climb trees. A similar vine which causes nasty rashes or blisters, or one with thorns, would be an excellent deterrent. Maybe a couple different varieties trained/pruned to grow under/on the lower outside edges of a Flet (or the underside of the branch a flet is on, depending on branch size). This would deter whatever large predators from the ground level might decide to climb a tree to get after the tasty humans, as well as other human raiders thinking of attack from below.
If there are no significant airborne predators the next step would be to remove branches (or even entire neighboring trees) which would provide cover/concealment for an enemy or predator trying to sneak up to your flets. The flet village (depending on the size of your tribes/size of your trees) could either be multiple flets on a single tree or several trees. This clearing would do double duty, since it would not only remove hiding places where something could sneak up on you, but it would also likely encourage the growth and wellbeing of the tree/s your flets are in! If you want added safety you could use the spiked vines or tree branches to weave the walls of their flets, or (if the foliage is dense enough) as a sort of floating wall around the village.
It seems like your branches are wide enough to provide rain cover. If you can fell the local trees/vegetation surrounding your flet you're not in much danger of attack from above, as humans/predators couldn't climb/jump over very well. If so, then you wouldn't need to do anything to the upper branches at all! If you can't cut down the neighboring trees, or if your weather doesn't often come with hurricane-force winds, then your flets would be built as high as possible to make it as difficult as possible for things to come in from above. If the tribal warfare is particularly fierce (or was in the past) they might build flets even higher than the large sheltering tree limbs at what I assume are mid-tree height. At that point they'd probably construct what amounts to treehouses using the thinner branches of the tree as key supports.
Another thing to note is they would, if at all possible, NOT cut into the tree their flet is in without REAL good cause. Any cut through the bark runs the risk of infecting the tree, so even if the trees have useful/edible sap they'd likely only drill into trees their not living in. Sure a big tree with a little hole isn't THAT likely to cause a rot that kills the tree, but it only takes a couple times in the millennia your people have lived in this forest for "don't cut your own tree" to become a piece of folklore passed down through generations.