So I tried it out...it could have gone better but it could have been worse. My Nikon D40 apparently doesn't have a video mode and my baby camera was out of batteries so I unfortunately couldn't film the first intro.
Setting: The living room where no rat's played before. I made oatmeal and chopped bits of apple up to put in it and set it in a bowl on the floor.
Phoe + Elphie: Not bad. Elphie was fairly persistent and a little rougher than I would have liked but it may have been normal? She insisted on thoroughly sniffing (or even grooming at one point) that just got rougher the more she got into it so I pulled her off.
Phoe + Brie: Not sure. Generally Brie wasn't interested. She'd sniff under Phoe's butt and also a little rough but didn't push it. Ten minutes later she had Phoe on her back and someone squeaked really loudly. Instinctively I swatted Brie off and checked Phoe over and there's not a mark on her so if she was bitten it wasn't hard. The manhandling of the baby had me on edge so I suppose that's why I jumped in so fast. : /
Overall the Dumbos were more interested in exploring and weren't all that interested in the new kid. Phoe let them do what they wanted. I was her "safe spot" so she was mostly on my lap therefore most of the interactions were on me. Near the end Phoe and Elphie were clambering over each other so I figured that was a positive enough note to end for the day.
I'll admit it's intimidating leaving them to their own devices even if I'm right there. Phoe is just so small and harmless. I can't imagine introducing a tiny baby to them! They'd probably sit on them.
Should I move the next intro to the tub or was that normal and I'm being paranoid?
Edit: Also...Brie left the room after I scolded her and when I eventually put Phoe back in her cage and was bringing Elphie back to hers, Brie was already in there, sulking in one of the hammocks.
Edit 2: Phoe was grooming herself a number of times throughout this whole thing so that's a good sign, right?