I've traveled with my mother, sister and brother before and my parents on another occasion. My mom and I get along great, so I just make my plans as usual. I work out my itinerary and then show it to her, saying "this is what WE'RE doing, you're welcome to join us if you like. If not, that's fine, too". Usually they'll join us on a meal or two, and on one or two of our park days (usually just for half a day or so). This works out well for us because they like lots of downtime and swimming on their vacations.
That said, I'm really happy that this trip is just us. I end up feeling responsible for everyone having a good time when we travel together, mostly because I made the plans and they all look to me to be their "Disney tour guide".
Now, my inlaws are another story. I would NOT want to travel with them. If we did, though, I would do the same thing - this is what we're doing, blah blah. They're more likely to be offended in some way over the whole thing, though. Plus, they're very cheap.