Rear camber can be fixed quite easy, but if your not sure what u are doing best to take it to a suspensions shop.

Lowering the coilovers to the max isn’t going to help with the camber, it maybe an advantage to have some negative camber. But this will increase tyre wear, and unless your car is a track car you wouldn’t want large amounts of it. How many degrees of negative camber do have at the moment?