small tank? not advisable to have these 2 tangs. Not impossible, but your tank has gotta be spacious for them both to coexist.
Always good to read up (google) before you purchase on their aggression or suitability.
Potential Solution: do a complete rescape, confuse both fish that this is a new environment. That could help.
Unless your sump has got sufficient rocks and space for both, i will advice against put them together in sump.
However, if you have a small tank and not enough rocks for them both (either to hide/create their territory), then i guess, pick one, and give away the other.
Just do some research before buying in future, it does help a lot.