Hi, Kyleen!
We've taken my parents, in-laws and several other families with us to Walt Disney World, so I completely understand your desire to have your own spaces. That's a great way to keep everyone happy while sharing the magic together...but not too together.
There are several ways for you to be able to maintain private space yet stay together in WDW. First, consider requesting adjoining rooms; this will enable you to open the door between two rooms when you want to, or shut the door when you need to do so. You could also look into a two-bedroom villa at any one of the
Disney Vacation Club Resorts. Frankly, this is one of the many reasons that we joined Disney Vacation Club, so that we would have more space when we travel to WDW...and it's been wonderful!
You could also get by with either a 1-bedroom DVC villa, or a Family Suite at
Disney's Art of Animation Resort or
Disney's All-Star Music Resort. The beauty of these is that there are two bathrooms as well as a mini-kitchen (in the Family Suites) or a full kitchen (in the 1-bedroom villas). You'll have a master bedroom which could be your mother-in-law's place to close the door and relax, while the three of you enjoy the living area, sofa / sleeper sofa and sleeper chair / convertible bed.
While it's great to vacation in WDW with just the immediate family, we love watching our kids experience the magic of Disney while grandparents get to watch and enjoy it, too. Some really special memories may be on your horizon, Kyleen; let's find you the right resort to make that happen!