I have a question, when it comes time to completly wean the colts, would it be sensible to put them in with Lightning, our stalion?
No. I can't imagine that would be good. There are circumstances where young bachelors are all turned out together, but they are all the same age. Your adult stallion is not compatible with foals. He should remain alone now until he's gelded. Stallions are not good companions to other horses, even 'good' ones. If he were in the wild, his instinct would be to drive the competition from herd.
NO - :)
NOOOOOOOOO!! Don't do that! Blade, who was only 2yrs old at the time, almost ate Bob alive, and Bob was a yearling.
Even geldings rough with the little guys sometimes