My 4-year old's behavior is becoming unbearable

I have my son on weekends. For the past year his behavior has become less toddler like and more bubbly and childish. This is the transition I adore most with children growing up. However, every time he comes back to my house a new stretch of bad habits arises. it started with screaming back, running away and not listening. Normal stuff. After a couple months it has transitioned into hitting usually punching and slapping in the face. I almost lost my cool when he slapped my mother in the face for trying to comb his hair. Full on pimp slap. Now not only does he scream but it is usually in regards to anything, completely refusing to abide by anything with no alternative or coaxing to solve his disobedience. A lot of times it is screaming for attention. If we talk with friends or family among ourselves he will scream at us for attention which if it isn't paid he will resort to hitting. He is even in the habit where he will hit my dog, a calm and submissive dog at that so I have to make sure my dog is also by my hip at all times. Hell no in my book. If i take my eyes off him he'll take food to himself. Goes into the fridge to try and drink directly from bottles, pull food from whatever he likes and start eating it while taking pieces he doesn't like and tossing it around the room. Now, I've worked with kids for a while as I have interned with schools and volunteered with children for years along with babysitting and being a part of raising a couple kids in my family so I know how it is sometimes. But he's showing some extreme dominance which becomes overwhelming considering I'm not into the nature of physically disciplining or intimidating him. I'm firm with discipline however. I am firm with timeouts and generous with removing whatever triggers this defensive behavior. I speak and talk with him about how it makes us feel which usually saddens him and puts him in place quickly. He does understand, he's a smart boy. Come Sunday, he is usually more relaxed and gets the picture but by the time he comes back the behavior is blown up again and more erratic every time. he gets constant attention here and I do not like this behavior at all, it intimidates me from taking him in public settings most times. My mother has gotten to the point where she tries to avoid being around him some weekends. Odd because she is old and has raised kids for most of her life along with being a teacher in multiple countries. Also sad because she was very adamant about being around him every weekend, even missing work in the process. His mother and I do not speak, in fact she refuses to speak with me which I feel would be crucial to isolating this behavior because I can't imagine that he does not act like this at home. Last year I pushed for a larger custody(Me for the week and her on weekends) but it didn't go in my favor even though she has no job or car and lives with her parents while I had my own job, car and house. I even went to pick him up once and she was drunk and hit me in the process because I refused to talk her while intoxicated and seemingly upset. He even cries and begs not to go home the whole hour ride back to mom's house. Sometimes i have to get her to rip him off of me just so he could go home. Now these may not make a bad parent. Playing devil's advocate here. But this behavior lately is really making me question what goes on at home and what i can do since I only have access to him on the weekends. I'm sorry for the long explanation but he starts school next year and I fear for him and his school. It wouldn't be fair to his teacher or classmates if he were to continue on like this. Also I just had another child with my wife and I don't want anyone else to face the same fate that my mom is right now. What should I do? What am I doing wrong? via /r/Parenting https://ift.tt/2LzNsfh