We can ask for prayer from anyone. Myself, I would stick to those whe have a pretty good idea are in heaven, like Elijah and Moses, (given the Transfiguration) rather than people we have no idea of like Adam, Eve and King David.
Not that they aren’t in heaven, but we have had no confirmation of it, as far as I know.
I’m sure if you prayed to someone who was not in heaven, a kind saint would hear your words and intercede for you.