The most important fact about pretty much all Pseudochromis species is that they are very territorial and will protect there homes viciously from any contender (no matter the size). So a key thing to think about is the size of your tank and how populated is it. I’ve had one rule a heavily populated 75 gallon reef tank. These guys are very elusive so once they are in, man they’re hard to get out! As for damsels, they may be fine when they are young but they get extremely beligerent with age. They are also both agressive feeders that seem unsuitable to a seahorse setup. Anyway just my input but I’d keep the Psuedos in a more agressive tank.