Thanks for the responses, everyone! I feel better about it, now. Hopefully we should hear about the chicks pretty soon! I don't know exactly the age difference but it should be under 2 months for sure. These are 2 weeks, now, and I want to say the new ones should hatch in the next week or 2 if I understood her correctly.
I think since it will be pretty warm out consistently in the next couple of weeks, I'll just move the older chicks into the coop when we get the new babies. They'll be a little young at maybe 4-5 weeks, but we'll put a heat lamp out there, and it will basically be SUMMER here (got a sunburn today working on the coop!).