I've led some church group backpacking trips, for teenage girls and their adult leaders who were also women. Sometimes there are girls or leaders with significant weight or fitness problems. I had to accept that these trips were not for me, but for the folks that wanted to come along, and plan accordingly with easier trails. I tried hard to make sure everyone knew what to expect, provided gear lists and rental options, ideas for food, held "practice" hikes for those who were interested, and had everyone bring packs to my house a couple days before the trip to check for fit and ridiculous/heavy extras. I make sure that I have enough adult leadership who I'm certain will be able to finish the trip, and an "extra" or two in case someone needs help to turn around and head back a half mile from the trailhead. I've never actually had that happen. I've been really surprised by the tenacity of some of the women who take these trips with me, who I thought were too out of shape and overweight to have hiked a mile. Most people don't want to be the one to hold everyone else up, and they don't want to fail in front of others. Most people also know their own limitations. In my experience, folks that really can't do it, don't sign up. No doubt there are exceptions, but I've never had a trip ruined by someone who just shouldn't have been there.
Sometimes there are people on the trips who decide they really love backpacking and would love to take on longer or more difficult trails, and we then plan future trips for them.