Others may have other things to say about it but ...
Honestly, I'd probably plan on pairs. I've had trios work, but it wasn't intentional on my part. I've also had it be a disaster (also not intentional).
And I'd also separate them EARLY into pairs, and separate them FAR. When they are up against each other, they are far too distracting. Especially if the goose you put in one pair likes the gander of the other pair better. The ganders will spend all their time trying to fight instead of taking care of their girls.
Everything is MUCH more peaceful and effective, for me, when I get a pair off by themselves and give them a place they want to nest. I keep failing to do that with the ENTIRE flock early enough, and I always regret it.
Also, when I have a good group of birds and no real plan, and they are unrelated, I let them do the choosing sometimes. If you have a place to remove pairs to when it becomes apparent who likes who, that works well.
I've heard of people raising large numbers of geese just by running them all together, but even with a larger flock that did NOT work for me.
I do have one group set up in front as a trio that is really too young to breed (eggs are infertile) but they are behaving quite well as a family (both girls setting tight on a shared nest, taking turns getting off, and the gander guarding them). I've given them eggs from other pairs to hatch out and I'll see what happens. And as I said, I've had it work before. But generally trios don't work well for me (unless maybe you give the geese separate and secure nesting areas - mine always choose to be close, and it's usually not a good outcome).
Good luck with them.
Oh, it CAN depend on your gander as well. The younger they are, the more willing they are to "spread themselves around" though they may do so ineffectively. In that case, I've had higher fertility by letting a small group live together (I have two cooperative ganders). Of course, then you don't know who the father is. But the older they get, the more exclusive they tend to be, and they may decide to only breed their favorite goose. You never know what they will decide.
Also, if you are planning to incubate the eggs, and not have the goose do it, you will probably not have the same kinds of problems I've faced. But I do think geese make the best incubators.
Good luck to you, whatever you decide.
