Sharing rooms with younger sibling

We just transitioned our 1 year old in with her 3 year old brother. He’s in a toddler bed and she’s in her crib. She naps twice a day still and goes to bed earlier than him. So, her first nap and bed time are super easy to get her to sleep. But afternoon nap is a nightmare between the two of them. I’m not sure who really is the problem either. They laugh, giggle, she throws her pacifier, he fetches it. I have to go in several times to reset them before they fall asleep. Anyone have this issue?!!

I don’t know if I should put one down first and let them fall asleep or what. I’m expecting baby #4 in less than a month and I’d like for this to be settled before babe comes. Any suggestions are appreciated!!