Grandmother problems

We have our 17 yr old grandson living with us. He hasn’t had the best upbringing. We raised him for 9 months when his mother went to prison. She always used the kids as a weapon against us. We hadn’t had any contact for nearly 4 yrs. Things became toxic for him to live at home, so he came to us. We are trying our best and we are helping him get to work and home, he also goes to school. We have even brought a little car for him, he has a after school job but doesn’t seem interested in going. He is the knowledge that he has to pay us back eventually. He doesnt seem grateful and has begun telling stupid lies and it is irritating me immensely. How do I try to get through to him about responsibilties without hurting his feelings.