How to convince my boyfriend to give my family a second chance?

My boyfriend and I are14, and I live with only my dad and my 2 older brothers. And they're total jerks to him. They're always making fun of him, and "playfully" punching him, and the most extreme actually sneaking up behind him and shaving off a chunk of hair from the back of his head with a pair of clippers. Because of this, he had to shave off the rest of his beautiful hair into a buzzcut. Before this friendly little joke, they took him on a trip to the island for 1 day and night or like a guys weekend or something, and they stole all his clothes while he was taking a shower so he had to go naked for several hrs until they gave them back. Now they even make fun of him for having a small dick.(it's not even small) so he Told me that not even a girl as perfect as me is worth a family that bad. But I've talked to my family, and they've promised me to change, but my boyfriend still won't take me back. Help????�