cars and legally binding contracts!?

[dame16]

i have this car that i have been paying for since september it is actually in my brother in laws name as it is being leased through the bank we both signed an agreement stating that i would be taking over the payments we did not get it notarized but we did have my sister sign as a witness as of right now since september i have been making the payments but i give him cash so there is really no proof that i am making the payments except for the fact that they are being paid but now he and my sister are deciding to get a divorce and from the looks of it looks like its not gonna be good he has already threatened to take my car so basically what my question is, is if he has legal right to take my vehicle even tho we have a signed agreement and i am making the payments. and if so would i be inclined to some sort of compensation on his part for the payments i have made over the last several months