For the vassal, crown authority 3 will stop him from taking territory from your other vassals.
But it won't stop his sub-vassals, it only applies to the king of Sweden as direct vassal.
Sweden is already my vassal
In that case... I agree with @Allen418, you have a very confusing realm going.
But I can give you the standard tools to deal with strong vassals: alliance through marriage, get dread to 100 and hope that the king of Sweden gets terrified, go diplomacy lifestyle and propose alliance without marriage, take befriend perk and make him a friend.
That's how you can keep him out of any faction.
Long-term I'd try to set up his heir in a marriage with someone from your dynasty, so that your dynasty gets the title. Then you can use your position as house/dynasty head to get a claim on this title.
Or provoke an uprising and win, that'll give you a reason to revoke his titles. Though I somehow doubt that you're strong enough for that, if your fear is said uprising in the first place. Sounds to me like you have a very limited personal domain and a weak army. You should consider doing something about it.