I have brought different families with us, and had different experiences with each. I almost always plan for a group of 11 or more. The most important thing we do, is we have 4 days to ourselves after everyone else leaves where we do whatever we want at the pace we want and see everything we missed.
With large groups, I am very clear with them that we are there to pack as much as we can into our days and they can join us for as much as they want or they can opt out of anything, but I really encourage them to meet up with us for FPP+ and the ADR’s. I make sure they are ok with me booking FPP+ for them, so they can ride with us. They have the option to use it or not.
If they seem to want to stick with us (and I have invited them and want to spend the time with them), I make a touring plan, but realize that we will not get to all the things. I put in some extra buffer, because they will always want to stop for a bathroom and a soda and a little snack on the way to try to rope drop FOP (this actually happened!!!) In those moments, I have to decide whether to leave them behind or do some major calming exercises and just go with it.
I usually also am clear at the start of the day that my family wants to see/do these certain things, and what time we plan to do them. Then they can opt in or out. Then throughout the day, I try to be flexible in between those things we want to catch, and you do have to allow more time for getting places, eating, etc.
I have found that most people want a little time for themselves to relax, so we make sure everyone knows it’s ok to separate or to get to the parks at different times. When they see how much more we did than they did, they might try harder the next day. One family took turns coming early with us and sleeping in depending on how tired their kids were, so I worked with them on which days were more important to rope drop, and then they went back early to get to bed the night before.
I have had some who want to keep up with my fast paced days, but they are still never quite as fast as we are on our own. When I have the extra 4 days on the end, I am much more relaxed with going at their pace.
One other note, it is actually harder on my husband to watch my precious plans get tossed to the side, and he gets very frustrated when we are wasting time waiting for people to catch up. I need to work on some calming exercises for him! I would say make sure to be open about your expectations, and let them know you want to spend time with them, but also want to get the most out of your vacation, and let them decide how much to join you. Then lower your expectations a lot. Sorry that got so long!