i'm not very good with genus's and scientific names so not sure if the ones we have fall into the groups you are thinking of, but as you've had no other responses i'll tell you about our in the hope it's helpful!!
however we have two blennies in our 30 gal and it works just fine.
one is a tail spot blenny and the other we have struggled to get a proper ID on, closest we have found in our research is a bi-colour however the lfs claim this is not what he is and insist he is a flame tail blenny, we've never been able to find a scientific name for him though.
however in terms of markings and temprement they are pretty different, the 'flame tail' is definatley more aggressive and is blue and yellow, the tail spot is much more of a softy and a nice orange colour with pretty markings. Initially there was some squabbling over territories however this was resolved within a few days and I think was really my fault for releasing them after acclimitisation at the same end of the tank. Good 3/4 months on and both get plenty of food, we never see any fighting anymore (flame tail occasionally bares his teeth at any other fish coming near his food but soon has plenty to eat and leaves everyone else to it) and they both seem quite happy.
