I read Here and it seems like you cant filter by username,
As for deleting/hiding the users, I read here that “there’s no way to delete messages from chat through a command” Unless a regular forum member has any ideas i would say your best bet is to report the users and have mods to delete messages and contact youtube support.
However ( and I don’t have any experience with youtube but…)
users do not see the excessive timeouts as read here
Sorry, I’m not being too helpful.