they are cleaning the rock as a potential spawning site. The female will lay eggs and the male will fertilize them. Not sure how long it will be since it could be tomorrow or 3 weeks from now. Once eggs are laid the female most likely will hover over them and fan them while the male guards the perimeter of the territory. the eggs should be kind of a amber color for about 3 - 4 days. if they turn white they are not fertile. the eggs will hatch and they will most likely dig a pit where they move the wigglers to. after a few days they should become free swimming. during that time they will make living in this tank very hard for the other 2 and chances are the pair might remove them for you (kill them) if they see them as a threat even though they are on the other side of the tank.
Also a Juripari, Frontosa and GT will all outgrow a 50 gallon tank and should be kept in something bigger for life