I'm so sorry you had to deal with this drama. My FI and I made it very clear in the beginning to all of our single friends, including his sisters, that they were not getting a +1 unless they were in a relationship with that person for more than 6 months prior to our wedding and we had built a relationship with that person. We also told people that it's a vacation and we want them to have fun, so if they decided to bring their +1, just know they weren't invited to share in the wedding or reception, since we had to pay for dinner and the chair rental and everything else for that person. Additionally, we told them that if they insisted on bringing that person down for the wedding and ceremony we would let them know the cost of adding that person and they would be responsible for it. So far, we haven't had any complaints but we have 10 months to go so I'm expecting some backlash down the line when new couples start up closer to the wedding date.