@Lennie The Redtail, Rainbow, and the Black shark are territorial. Must be provided with proper space or will harass other fish not just conspecific aggressive.
I don't know about multiple pairs with the exception of the Shellies. Possibly a harem with a Apistogramma specie. Had a pair Double Orange Flash Apistogramma that claimed a 20 long for territory.
Depending on the specie of fry most of my aquariums has plant's or algae.
This helps because fry will seek out the microorganisms that we can't see lol. Not saying not to feed but a extra food source. I hope you sort everything out with your fry.