i have an above ground pool for my lizards and this is how i set it up:
door in the side with another door on inside so you can go through one door close that and then open the other.
for the covering i went to a local avairy factory and had them custom a wire roof and they made it a perfect shape and fit and enough to over lap the side so i could drill into the side and stick it in place.
instead of africans heat mat idea,where the filter and other pipes used to go i have put basking lights in but like you said you will not be needing this for your pool.
make sure there is lots of rocks and i even planted some trees and little bushes but this needs maintainance every now and then.
you should make sure there is absolutely no way that lizards can get or anything else besides yourself that can get in.
blueys and beardies should be fine together as long as they are well fed and there is not to much of a size difference.
any more questions i would be glad to answer
