Siblings and fighting

Anna

What do y’all do with siblings that fight a lot. I know it’s normal but I can’t take anymore of it. My son is gonna be 4 and my step daughter is 7. My son is constantly asking for his sister but on the weekends she’s here they just fight about everything. Literally I ask my son to grab a water for me and my daughter will run and snatch one before he can so now he’s crying and they are fighting. Or my son will hear my my boyfriend pull in after work and will run to open the door like he does every night but my daughter will see him get up from the couch and beat him to it every time so now they are fighting again, fighting over who gets what plate and who sits where on the couch and over who gets the blue pen and who gets the red. Literally everything. My boyfriends ex wife has been out of state for the last two weeks on a family emergency so my daughter has been staying with us. So it’s just been 10 straight days of fighting. My boyfriend works long hours so he isn’t home for most of it and just says it’s normal when he gets home. Which again I get it normal but doesn’t make it any less annoying. They are literally fighting like yelling fighting over wether or not the timer says ThreeZero or Thirty. Like who f*ckin cares. But no today was my last straw I had a feminine emergency while I was out running errands, instead of heading straight home I went and got them from the babysitter. Explained to them I had an emergency and that as soon as we got home I had to go straight to the bathroom and that I would be in there for a minute. They both in the car ride over said they wanted to play video games. We have two TVs right next to each both with consoles and both with the same games for this literal reason! And the entire time I’m in the bathroom they are screaming at each other over who gets what TV. I sent them both to their rooms. I told them they couldn’t hang out in the living room anymore which of course I caved because my daughter is leaving tomorrow and my mom guilt over my son being sad that he misses his sister tomorrow kicked in. What do y’all do when your kids fight?