I would increase the size of the brooder and combine them now. It is usually safe to combine chicks when all are under one month old. If they are attacking one another to the point of drawing blood, they may simply need a bunch more space, and quite possibly, less heat. At that age they should have a minimum of 1 sq ft per chick, not counting space for food, etc., and will need twice that in a couple of weeks. They should be able to get away from the heat, or move under it, as they wish. You can put a few things in there to distract them -- a low "roost," a brick or box to jump up on, something to hide in, etc. Bring them a small piece of sod from outdoors. A refrigerator shipping box or the like makes a good brooder, and is disposable, to boot! Take them for short outings outdoors when the sun is out - just set up some sort of temporary pen if needed. Chances are, you can move them to their coop in 2 or 3 weeks, maybe sooner. Give them a bunch of hay to snuggle into.