like g40steve has said i would check that this is not going to affect you in anyway as being family he might just have said to the copper on the night "no its not mine officer but its my brothers an he said i could do it" so in which case it might be your fault for letting him out without insurance, id also tell the police it was taken without owners consent, yea its grassin ya lil bro up but the little so an so should not have touch your pride an possesion. I know i would tell em.
Take some thing of his or some thing that is worth loads or alot of items an sell them to make up for the repairs of what you need done an then take some more for good measures, id kill the little s**t or kill his bloody van.