Welcome to BYC!
EE's are pretty broody, so I think you will have some broodies in your group. RIR's are considered standard in broodiness. Not as broody as EE's, but can go broody as well. Do you have a rooster for fertile eggs?
Good luck with your flock and welcome to ours!
Yes, EE hens will brood, however, many of them do not. Last spring I raised 22 EE hens and as of date, only one has chose to go broody. I must say that those that do brood make great moms. This hen just hatched 9 Pheasant eggs and loves those babies.
If you want to hatch EE eggs when your young hens began to lay, I would suggest purchasing a couple of banham hens to hatch the EE eggs. Banhams are known for their brooding nature.
RIRs are not great brooder as thery are bred for production of eggs. Although, some will brood. I have one that acts if she will brood but never becomes so broody as to incubate eggs. She quits the nest.
Gotta love the EEs !!!