How exactly going over limit of compedium sharing works?

So I have this case: I'm a DM, I have 12 players in one game and have a free account. We play one-shots, so on every session there is max. 4 players plus me. I want to buy PHB, so the players can access all of its subclasses, spells, feats etc. from charactermacer. If I share PBH with first 5 players, let them make a character sheet and then disabled the sharing, so I can give it to another 5 players, will the changes in the character sheets of the players, who don't have a access to PBH dissappear? 

Once data is on a sheet, it does not have any link back to anything. It's just text or numbers. If the players made their characters in your game, as opposed to the Roll20 characters feature, their characters sheets will remain intact. If they made them in Roll20 Characters, their characters will return to that feature and need to be re-added to the game when they are invited back. Note that turning sharing on and off will not control who has access to your compendiums. Once you exceed the number of people you can share with, the only way to add a new person is to kick the old one from the game (even temporarily). From the Help Center: What happens if I go over my limit? Once your game exceeds the maximum number of players, compendium sharing will be disabled and you will get a warning message that the feature has been disabled for this game. You can use the "Kick from Game" feature to remove inactive players from your game or upgrade your subscription if you need more players to have access to your compendium. The limit applies regardless of whether the players themselves own the compendiums you wish to share. Players who have purchased the compendium will still be able to access it as normal for themselves, but other players won't be able to access the shared compendium in a game they did not create.

They made the characters in my game. I think the best option here is to change their character sheets myself, right?

It's up to you, as to which you think feels less clunky. Kicking and reinviting, or making changes yourself. Be sure to let your players know that if you go the kicking route, when a player is kicked from a game, the URL changes, for security. Players who remain in the game can still get to the game via "My Games" on the Roll20 site, but anyone relying on a bookmark will need to update.