It's possible to keep two different pairs of some species of clownfish in a 90-gal tank but I wouldn't recommend it. It's certainly possible once you get into a tank that is 6-ft long, such as a 135-gal tank or larger. Be forewarned that some of the larger species can be rather aggressive, especially Maroon clowns (
Premnas biaculeatus).
B/W clowns doesn't really describe a species, just a coloration; therefore, it's impossible to say whether they would get along with any other species without knowing for sure what you're talking about.
Nowadays, most people who use the description "B/W clown" are probably referring to either
Amphiprion percula or
A. ocellaris, although there are other species that can be black and white in coloration.
There is a black color morph of
A. ocellaris that is found off the coast of Darwin, Australia. It's just a local color morph of Ocellaris clowns. Then there is a black and white color morph of
A. percula that is being captive-bred and often referred to by the name "Onyx clown."
You can find both Percula clowns and Ocellaris clowns available that are black and white in coloration. Obviously the color makes no difference when pairing up two fish of the same species. If you put two Percula clowns into the same 90-gal tank, they will likely form a mated pair eventually even if their coloration is different. The same goes for two Ocellaris clowns of different colors. It's the species that matters, not the coloration. Of course, all of this assumes that we're talking about two sexually immature juveniles and not two fish that have already progressed to female, the terminal phase for all clownfish, which are all protandrous hermaphrodites. Once a female, always a female. A female clownfish cannot change back to male. Putting two female clownfish of the same species into the same 90-gal tank would be a recipe for trouble. Big trouble!
Many of the clownfish species can and do crossbreed in the wild to form hybrid offspring. Some hobbyists have tried their hand at crossbreeding in captivity, expecially with Percula and Ocellaris clowns. These two species will often pair up in captivity if there isn't another conspecific available. Their ranges do not overlap in nature, but if you put one Percula clown and one Ocellaris clown into the same tank, there is a good chance that they will form a mated pair, assuming they were not both already females.
If you successfully raise the offspring of such a pairing, you will have Percularis clowns and they
will be fertile. The coloration and markings of the offspring will be an unpredictable combination of both parents. In other words, if you get two dozen babies to survive, they might all be slightly different.
That's not something that I would recommend but it has happened.
For a 90-gal tank, I think you would be better off choosing two juveniles (or a mated pair) of the same species.
Good luck!
