Brennan isn't sharing a room with Cate yet. In fact, he'll probably be in with Mommy and Daddy until he sleeps pretty solidly through the night. One baby up in the middle of the night is enough for us. But I do put Brennan in his crib every few days or so. Sometimes it's so I can help Cate get dressed. Other times it's while Cate and I snuggle together during naptime (he stays quiet for the most part). Still other times it's while I put away their laundry or clean up some of the books and games we've moved in there.
While Cate still has her moments where she wants someone else to take Brennan or home or wants him to go back in my belly, she's starting to get more curious about how to care for him. When he cries, she says "It's okay buddy." She tries to put his pacifier in his mouth when he loses it. She watches while I change his diaper and tells him "Shhh" (he pretty much hates having his diaper changed. Probably because it's cold.
But mostly, she just watches. I find her many times throughout the day just staring at her new little brother. Much like I find myself doing too.