He marked up really nice for spawning.
Maybe just removing the pleco instead will save the eggs and be less stressful on the parents. I wouldn't move them until the fry were free swimming. Is there anything other than the pleco in the tank that will try to eat the eggs or fry?
I've never had good luck moving parents with the fry. They usually get stressed and eat them. You could just wait until you have wrigglers then siphon them out. That's what I always do. Hang a net breeder in the empty 20 gallon and put the wrigglers in that. It will keep them from rolling around the tank bottom. Once they go free-swimming in the net breeder, you can feed them and then release them into the tank after a day or two.
If the parents are tending the eggs, they should have no problem keeping a Pleco or other tankmates away, especially with such a secluded cave entrance.