Yes your idea is good. Put the second set of chicks under heat lamp with food & water. When broody #2 has hatched her remaining eggs, put the older chicks back with her at night, & do so before she has gotten a good look at her younger chicks. When broody #2 takes all her chicks out the next morn for the first time & shows them where the food is, she will be very impressed at how smart her chicks are, that they already know how to find food!
im laughing, but i have used the above scenario many times each year. In my case, i get chicks of breeds i want from the feedstore or a hatchery, and wait for a broody to hatch her own chicks. I then then slip the feedstore chicks in with her at night, before she ever takes her own chicks out of the nestbox. Has worked every time!
