Okay, let me explain. :P Or rather, give the short version.
Angels are all born from the Ancients, and although Chaos was an ancient too, his offspring are far from angelic.
The forces that these angels are fighting are creatures, beings, barely worthy of being called anything beyond that. Think… the heartless of Kingdom Hearts.
These creatures just want to wreck havoc on the earth, and anywhere they go, so it's the angels' jobs to stop them.
So no, the angels don't fight each other, and they don't fight demons. They fend off creatures, and unbeknown to them big bad stuff is about to go down very soon (well… depending on how fast the RP moves)