I don't know, there are people that say breeding trios are risky and the moms could get jealous and try to steal or even kill the others joeys.
As far as adding a neutered male to the mix, it would be better to keep one of the male joeys and neuter him and leave him with the family.
Feathers-Sweetie, Sklyar Blue, Mister Peanut, Big Mack & Ibo
Fur-Widget, Gadget, Guinan, Mr. Spock, T'Mir, Micheal, Flower & Pappy
T'Pol, Pandora, Elizabeth & Curzon
TY, TJ & T'Pring
Forever in my heart, Gizmo, Tucker and the rest of my babies over the