They will have different temperature requirement with 3 week age difference between them, if I did my math right.
When I added a new chick 2 new chicks (same age) to 3 two week old's that were established in the brooder already, it wasn't pretty. So I added 3 more, switched to a red light, and moved thing around in there. Peace ensued. Next brood gets "mamma heating pad".
The way they pile on top of each other I would worry about the little one getting trampled, if not bullied.
I have read that if you add them when they are sleeping it is smoother.
So I think it kind of depends on your set up and your individual chicks. We have 1 named Atilla for a reason.
Unless you have a good plan for integration in the future, I would refrain from staggered hatches like that. Seems like it would be less stressful for both you and the chicks. JMO
Good luck with your last 1!