25 UK gallons equals 30 US gallons. I would be more concerned with the height. Minimum is 16" for standard fin angels, 18" for veils.
Angels will nip other fish, the more they look like angels, the more likely they are to get nipped. Pairing & spawning angels will nip & chase most any fish out of the territory they have claimed.
I've seen dime body size angels nip the dorsal of a foot long common plec. I swear they did it just to piss him off. Reminded me of a kid poking an elephant with a stick.