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.
I've personally had Senegal bichir spawn with 2 different groups. The most important thing is observing them daily. You have to collect the eggs asap or the adults will eat them. Unfortunately I couldn't keep the fry alive 😕
If I decide to try to raise fry again I will be ready hopefully.
https://www.monsterfishkeepers.com/forums/threads/senegal-bichirs-spawned-d.650595/
Lighting for plants depends on what plants because some species such as Anubius,Java Fern, and Java Moss don't require bright light.
I personally prefer sand but it's your preference.
Have a young pair that I ordered from the Wetspot Tropical Fish.
The pipefish spawned about 3 weeks ago. Don't think the eggs were placed properly or secured because the eggs all released prematurely. This time noticed a difference of the pouch looks covered 😆
Oh okay if the worms glide across the glass glass they are planaria. Do you have a magnifying glass on hand? If so observe closely and if planaria they will have a triangular shaped head.
Did you collect the bladder worms yourself?