We travel with other friends/families all the time (we're DVC), and my best advice to you starting out is to book 1 meal a day together at a nice table service restaurant.
That way you know you are meeting up with them at least 1 time a day.
Also, create an itinerary for your family and give it to the other family and tell them, this is where we'll be at this time and this day, you're welcome to do as much or as little with us as you'd like, but you know where we are

.
We've had families that followed us to the letter, and families that we never saw except at the one meal a day, and both ways worked well for us.
Because really, you're not on vacation for *them*, you're there to make yourself happy.
This, for us, has been the best way of making sure we don't sacrifice our enjoyment or comfort trying to please other people, and they don't feel left out.