Your BF's home and your BF's kids...so he needs to be the one to discipline them. Unfortunately many dad's don't want to be the bad guy when they have the kids with them, not realizing that teaching their children respect & responsibility actually benefits their children and aids them in their progression towards adulthood.
I'm sure living with these boys, you've come to care about them. Let your BF know that. Talk to your BF about it calmly without giving the feeling that you are just criticizing his kids because then he'll only become defensive of them.
Best of luck
