Everyone has a relative or two that doesn’t always behave. Generally if it is a close relative you need to invite them. Enlist a close friend or family member to help keep an eye on them and relax and enjoy your day anyway. If alcohol is a contributing factor consider setting up a limit with the bartender. If the problem is a significant other for someone you can’t get around giving a plus one, then be candid, but polite, with them. Let your guest know that they are responsible for whoever they bring and if there is a repeat of cousin Julie’s wedding you will have to ask them both to leave. Though we all hope it will never come to it, you can always have your ushers, well usher, the offending party out of the event.