I would check out 2 things. First, make sure they are berghia nudibranchs, a breeding pair. Then go to inlandaquatics.com and read the section on culturing them. he biggest challenge is to have a reliable ongoing supply of aiptasias for them to eat, preferable NOT attached to rocks. That way you can get a whole colony of them growing in either a small aquarium or a couple of big jars. Then, the best way to use them is to cycle aiptasia infested rocks into the aquarium where you're keeping them. Just releasing the pair of nudibranchs into a large aquarium is probably not going to work; there are many animals that will eat the nudibranchs, especially juveniles.