T.L.
Hi S.
I think the boys should ok with cinderella coming in if you are that worried about it you may want to get some trucks or cars and a few books and have them avaliable to play with if they are not interested.
as for the baby I would buy a sling and have him in that or a front carrier so you still have baby but your hands are free. Have a great birthday party. I made my daughter a castle cake when we did the princess theme.