I would brood the goslings yourself for at least three weeks. Yeah I know, it's messy. But it's insurance against losing any of them to the inexperienced parenting of juvenile adults.
Usually, even juvenile geese have strong parenting instincts. I would put the babies in a pen for a few hours a day outside and see how the juvenile geese behave around them. If they hover around the pen, hold their heads down near the babies, and maybe even get nasty with YOU when you approach, they will be willing to parent the goslings. I would not turn them loose with the juveniles for three weeks, though. It would be like allowing your ten year olds to take full responsibility for an infant.
That's just what I would do, I'm all for letting geese parent their goslings, but I'm sort of a worry wart nut about what could happen to the babies.