You have a choice:
1. Roll your Stamina + Primal Urge. The number of successes equals the number of forms you can morph through (not including the one you started in). For instance, to get from Homid to Crinos needs 2 successes. This takes 1 combat turn. If you don't get enough successes to get to the form you wanted, you'll have to roll again next turn. Clothes will burst their seams, get ripped, etc.
2. Spend 1 Rage point for an instant transformation. Clothes will be totally shredded.
3. Some folk bought the Metamorph merit which gives instant transformation without spending Rage. Clothes shredded.
To get into the spirit world, the party has a choice:
1. Everyone rolls individually against their Gnosis. (You can spend a Willpower as normal). Anyone who gets zero successes can't try again for an hour of game time, unless they want to make a One Chance dice roll. If they botch that, they'll get stuck halfway through.
2. Nominate someone to pull other pack members through with them. Everyone has to abide by that person's roll. So if they screw up it affects everyone they were trying to 'carry'. You can only 'carry' members of your own pack this way - it doesn't work on other folks.
You can mix and match the above, with some people rolling individually and some being carried.
Leaving the spirit world doesn't require a dice roll. But the geometry of the spirit world means that sometimes you are not near enough to the real world to step back into it.