Adding on to what @ChristopherM is saying, you could always use decorators to sync lock states between clients.
Edit: I’m an idiot and didn’t read the post properly, I managed to get decorators working in my brake lights script, you could look at that and see if it helps. You could set a decorator on the player’s vehicle, then run a check for when another player tries to get in the vehicle, grab the state of the decorator and just either allow or deny the attempted entry.
Here is a link: [Release] Vehicle Brake Lights [1.0.2] [Client Sync] (Updated 2019)