I recommend following mo mommies on Insta she is great about this stuff. I’m pregnant and have a 3 year old that still tantrums and acts out and we do time out but to us that means going upstairs staying in bed and calming down with us near and talking about our emotions. He says “I want a time out” which means he wants to calm down. As for the sibling I have no advice just kinda worried now haha my kid is the same all attention on him and gets annoyed easily.

1. Create a yes space for both kids, cordoned off to their sibiling. They can touch/play with anything in their yes space, and it is safe from their sibling.
2. Start praising the heck out of your older child for every single skill your baby gains - sitting up, rolling ball, eating with a spoon, reading books, drinking water - whatever. "Oh, Larlo! Larlita is sitting up! You must have taught her that. Nice work!"
3. When he is calm and you all are together alone, start talking with him about how he feels about having a sibling. "Larlo - I noticed you hit Larla this morning. Were you feeling angry? Can you tell me about it"? Let him have his feelings. Let him say mean things, or sad things, or whatever. Then, "Larlo, I get mad sometimes too. I also don't like to share. I won't let you hit though. What else can we do??"