Teenagers need their own social lives. Despite doing the same extracurricular activity for nearly our whole childhoods, my sister and I were rarely forced to include each other in our social lives. By the time we were over 13, we had our own things going on, which worked for us. If I were forced to take her to my hangouts with friends she didn’t know, we both probably would’ve resented that. It might be hard as a parent to see one kid have a vibrant social life while the others don’t, but the solution to that problem isn’t to fumble the social life of the kid with a social life. You should find out what kids without friends like to do and help them thrive within their age group. If you force a 15-year-old to hang out with his younger sisters constantly he’ll resent it, and that’s exactly what happened here.