S.H.
We just put my son in a big boy bed two months ago and he just turned 3 last week. He is my fourth child so I knew what I was getting myself into BUT it's been challenging to say the least. We needed to because he's potty trained now and he needs to be able to go to the bathroom. This morning he woke me up at 4:00 and this is a common occurance now that he can get out of his own bed. It's exhausting but they need to learn too. My oldest was in a big boy bed at about 20 months but we also had a 2 month old at that time so he was kind of pushed out of his bed.
Good luck to you! I can't imagine doing it with two. Just remember there is no rush into this. Don't feel like you need to do it if you (or the kids) aren't ready.