1. Well, by us, everyone is more than happy to tell what they’ve learned, so I can’t really help you there… Maybe ask them individually all throughout, if they have something to add.
2.When there’s a lot of kids it can get quite tricky bc you want them each to feel like their divrei torah are being treasured and listened to. I suggest each picking out a few things to say, the BEST of what they’ve learned, and that way, the Seder wont go on forever (works in our house)
Same divrei torah-wise, um, that could be an issue. Depending on the age of the kids, maybe they can do a bit of research before-hand to try find something that they’ve never heard before.
From my experience, my younger siblings sometimes say what I know that I or another one of my siblings have said in previous years, but we make them feel as if it’s the first time that we’ve heard it 🙂