i usually just feed them pre processed liquid small fry food (wardley brand) until they reach a size big enough to eat finely crushed up pellets. some people feed baby shrimp and stuff like that, but ive done allright just with the liquid stuff, i think its egg based.
Ive seen the male take over the parenting role before. its hard to tell what will happen, its not an exact science. sometimes the mother will do all the caring and the male will ignore them, sometimes they both seem to care for them or the male takes over. there are alot of variables, sometimes the male will kill the female awhile after they have hatched and sometimes they will be fine together or sometimes the male will eat the fry for no aparent reason. so its hard to say whats normal and not normal behavior. why did you choose to split the batch in half? i imagine the devil in your tank will end up eating the convict fry one way or another eventually.