The parents will care for the fry, so dont worry about that, you dont really need to do any more water changes providing you are already doing weekly changes, changing the routine may upset the parents and cause them to eat their young, not likely but could.
I would hold off introducing the angels as this will really annoy the parents, who will see them as a threat and could bully them. You may well find you need another tank to remove these fry too once they are larger as the parents will do doubt spawn again.