angels and roselines are fine together. i used to keep them with altum angels. like other said. 50g cube is pretty small for them. since they are fast swimmers. they do prefer more swimming space. however, in my opinion you can get away with it if the tank isnt going to be heavily planted. i say go for it if you want them. as long as you take good care of them i dont think they mind living in a smaller tank. better then in small tanks at fish stores and where they were raised.