With my new arrivals, I introduce them over a period of a few days, and segregate them periodically, like if one of the Bengals is threatening to eat them ... but usually after a few days I'll let them start to roam the house. It's pretty standard, at least for my crew, for them to be completely timid and scared the first day or two.. sometimes it takes a little longer. The Pogue didn't come out and start exploring for a good three days.
After they start roaming the house.. but they're still little, I'll lock them up when ever I leave the house, but let them roam when I'm home. Basically, locking them up when they're unsupervised.
I can't really help with the diet, as my old(er) cat and my kitten and the ones in between all get the same diet. (And the reason for that is, just so you don't think I'm nuts.. is that they are on a raw diet, supplemented with a high-protein no grains dry.. and that's recommended for all stages of life, as compared to the commercial foods) So, guess I still might be crazy, but now at least there's an understanding into the reasoning.
When we fed different types of food... we segregated them during feeding time. And if you're free feeding dry, pick the dry up and only feed it at certain times, or... pick it up for a few hours before you feed the babies, so they're hungry, and will eat their kitten food. I don't necessarily think that it's a bad thing if they get the other food.. as long as they're getting their "kitten nutrients" as well. Just my personal opinion.. but the breeders on here know more about that I'm sure, or sharky.. who knows nutrition better than I do.
Best of luck, and they're gorgeous!!