I think all of the mentioned verbs are in the same class, because they all inflect irregularly in the same way: -aimasu for the polite form rather than -arimasu.
My question is how these verbs were formed. My guess is there is some base verb which was connected to aru and then underwent some sort of devoicing and 音便.
For example, does くださる originate from 下す + 在る?
If this guess is correct, does this 在る have some semantic meaning? (There seems to be a large chance that it's used to make things more polite, since these are all 敬語.)