Our Guild protocols always suggested members find the captain and get crewed, ASAP. Not only good manners, but you start getting bonuses sooner. If I'm captain, I am always checking the deck for new uncrewed. And I will put them on notice if they deny it.
When I head up a crew - first thing I state to newcomers. Captain has the helm, unless I ask if someone would like to and even then only if I think they can handle it. Happy to help a mate earn some sailing rep, but not at the cost of a full cargo hold...
As for the bad behavior, sometimes you might not have an option but to do the quick maroon stop for people who aren't willing to join your crew and being a nuisance.
Simply make sure the people you WANT to keep are crewed. Then, turn off all but Crew option. Hit a wild island and then immediately relaunch.