im 16 so idk if this will help any but ill try ... are u close to your grandson if u are mabey u could talk to him on how he is feeling/why he dont eat or even a list of his fav foods so u could cook them for him when hes with u somthing to let him know that he is cared for mabey u could try and see if u can switch the poster with a dry erase board so he can cheak off the things he needs to do and try to have a reward if u can ... could u talk to his stepmom about this also about your son drinking its REALY not a good idea to have beer and stuff when your grandson gets to be a teen .... if your son drinks to much he could snap easy aswell what i do for my nephew who is like 11 i get him a goody bag of stuff from the dollor store and he loves it every time .... hope i was a little help hugs