Returning a new car

[catsjh]

I signed for my daughter and son-in-law (my son-in-law was the co-signer) for a new car awhile ago. After a year they could no longer make the payments and I wasn't in the financial position any longer to make their payments for them. I thought a "voluntary repo" would be the best way to go. After many, many phone calls their attorney talked me into paying them $25.00 per month "to keep it out of court". These payments are expected to be paid by me until the $8000 car is paid off (well after I have left the earth). So...how is it that the car company can continue to take my money as well as the money of the present owner?
Thanks for the advice!