She'll have to be integrated carefully.
Keep her in an adjacent but separate enclosure.
Maybe add the most docile older bird in with her after a week,
mix and match until you get one that will get along.
After a week of that, add another.
This might help...
The broody would not be happy with a 'strange' bird in her space, it may even break her broodiness.
How old are these birds..and where do they reside now?
I'd start integrating the serama and the bantams now by putting them in separate but adjacent enclosures.