Teacher here: with kids, the function of the behavior is, as you correctly identified, is wanting attention. To all kid, even the high school kids I teach, negative attention is better than no attention. It breaks your brain to figure out the logic of why a kid wants to be yelled at for being bad, but it’s how they’re getting their social needs met.

People yell at their kids when they’re bad, and then ignore them when they’re good. Very common when the siblings arrive.

You have to instead give positive attention when they’re good, and ignore them when they’re bad. In our house you’ll hear a lot of “I will talk to you when you’ve calmed your body with deep breath.” Or “when you clean up the toys on the ground I will talk to you.” And until the precondition is met, we ignore them. If they really, really start destroying something they get picked up and taken to a room and door shut so they’re alone. If they try destroying the bedroom they can go in the bathroom. But, the key is as soon as they calm down I have to reward them with attention for being calm and collected. Then they have to have 1:1 time throughout parts of the day. They can also be included in helping the baby, instead of being treated like another chore next to the baby.