I have 2 clowns that have been together for about a year in a 90g, LFS is selling very small baby clowns and wanted to get 2 more .. but will the bigger older ones kill the smaller ones ?
Most likely not a good idea trying to add another pair as you'll probably end up with your two original clowns. You may get lucky but I think the odds are against it. My $.02 anyway.
Gonna knock on wood here before I say this but I've been very luck with clowns, added multiple designer clowns and so far so good, they all hang out together