Damsels are pushy, but can work woth other fish if there's enough space. Thereæs always a chance it won't work , especially with the 3 spots (incredibly aggressive!) and striped humbugs.
Seahorses are easy to keep in some ways, and very hard in others. They don't need much in the way of setup - they have a low metabolic rate, don't move much, and when I've seen their relatives pipefish in the wild, lets say the water quality isn't pristine. So they can work in small tanks. However, they are difficult to feed. They require continuous amounts of small, often live food. Live caught are very difficult to deal withI believe - realistically you need a large 'refugium' style tank to provide copepods else they'll simply starve. Brine shrimp will be accepted , but are nutritinally crap - again the fish will starve to death, but this time with a full belly.
Absolut - how's your angel? I hope you have a nice lve rock tank or you might have some fun getting that to eat as well. Unfortunately I suspect by now the damsels will have 'done a job' on it - it sounds like it was getting a beating.