Need advice

Back story. My son is 4, my step daughter is 8. There is 6 kids in total but the focus is these two. Iv been in my step daughters life since she was 3. My son was obviously born shortly after that. She’s always been awful to him, spoiled doesn’t like to share ect. She literally used to play a “game” when she came over where she’s grab all my sons toys and place them somewhere he couldn’t reach and refuse to give him any of them. Opening his presents on his birthday, Christmas ect. Now my son is getting older and it’s leading to more and more issues. She is extremely bossy with him. If I say something off hand like “hey I need these toys to get picked up” she’ll immediately get off the couch and turn the x box off on him mid game and be like “your mom said to pick up the toys. Why aren’t you getting up get up right now.”

Lately my son has been biting his nails, and she’ll just rip his hand out of his mouth when ever she sees him. Like will stop what she’s doing to run to the other side of the room to snatch his hand out of his mouth. Doesn’t say anything to him just rips his hand from his mouth. Then he’ll hit her and she’ll be screaming for me like “aren’t the rules we keep our hands to ourself” like yes but also includes you. Then she’ll pout and tell her dad I was mean to her when he gets home. If I pick them up from daycare she’ll literally be blocking the exit and pushing him back “no you are not leaving with out a coat.” And it’s that time of year where I know it was 30 and raining when their dad dropped them off but it’s 65 and sunny now. And me and the staff will be like “he doesn’t need a coat.” And she’ll be like “no he’s not leaving with out a coat.” Like who really f*ckings cares it’s not you whose gonna be cold at the end of the day. It’s bizarre. If we go to a park the whole time it’s “your son is doing this” or “your son is doing that.” Like yes I have two eyes myself. How about you go play yourself. We went to the park the other day and I brought some toys, cheap toys I could careless if they get lost. Anytime my son would walk away from them for a second she’d immediately start picking them up. And I explained several times that I wouldn’t have brought stuff to the park if I didn’t want it to get lost, that it’s perfectly ok for other kids to play with them. In one ear out the other kept picking up. Trying to get back to car after the park my son was running and the time she’s yelling “your too far.” “Stop running” meanwhile I can see my son fine and he’s running cuz I forgot to bring the water bottles up the park and he’s thirsty. If I say anything about it to my boyfriend he’ll be like “she’s just trying to help”

I feel like when she’s here all I do is walk around going “leave him alone….leave him alone…..please leave him alone.”

I had a very over barring sister growing up and we don’t even speak now cuz I spent most of my childhood yelling at her that she wasn’t my mom.

I don’t want my son to have this experience but I also feel like I’m running out of ways to tell her to relax

Any of y’all have kids like this? What do you guys do?

Also she’s here every other weekend and her mom lives across town so there isn’t a strict schedule. Sometimes she comes a day early or stays a day late. Sometimes she’s here on a random Wednesday. All that’s fine. But when she’s not here and with the way my husband works. It’s just me and my son home most days. So if he wants this for dinner, I cook it. If he wants the big tv he gets it. If he wants to pick up his room in an hour then he gets an hour. Obviously can’t be like this when his sister is over but I feel like it’s extremely jarring to go from running the house to “you can’t wear that. No you can’t have a snack. Pick that up now.” When she’s here and it’s not even me yelling at him.