Haha, wow. You really did pick the most hostile place in the solar system for your aliens^^
Here is a video that explains why Venus is evil. Pure evil. https://www.youtube.com/watch?v=c6K2ibg-Wb0
The planet essentially baked itself dry. There is nothing there that could sustain life.
Even Mars would be better than Venus.
If you want some kind of subterranean culture I'd choose one of the bigger moons of the gas giants. Those are said to have underground oceans! I mean, that is a place where scientists actually do speculate that life could be found there^^
Did you not read the part where I said "survive temperatures of 800 degrees celsius"?
After all, they're aliens, and they're biology would likely be hella different from ours.