Okay its been three days

So in the beginning of the year like Feb. I got a car and up until July I was able to make the payments, now that I have no job I can't make the payments anymore so my oldest brother R has taken over payments. So the payment on the car is $300 every 13th of every month for the next two years, well his first payment he was 13 days late. Now he is late again and I'm afraid that its going to mess up my credit a lot, I made him sign a contract saying that if he isn't able to make the payments I will make them for him and until he pays me back I will have custody of the car. Now I talked to my sis and she made it seem like I was being a bad guy for wanting to do that in order to protect my credit. My mother on the other hand told me to do what I need to do, I love my brother but honestly he isn't the most reliable guy in the world. I'm glad i made him sign a contract even though he is blood because he isn't concerned with my credit just the hood rats he sleeps with. If anyone is reading this can you please give me your insight to this topic. How do I deal with getting my brother to pay up with out fucking up our brotherly bonds?