Have you checked the hotels in Granbury yet? They have a few hotels. I'm not sure if they have a suite, which is what you would need. Fossil Rim has sleeping arrangements, I'm not sure how much though. I've never stayed in Granbury or near Fossil Rim.
Fossil Rim, I've been a couple of times. I would recommend not going there on a really hot day. I've been there when it is 90 and 100 degrees, it seems like it is a waste of money. The animals are all hot and they go under the trees and hang out there. We had very few animals that came to our door/window for food. I would recommend going in the morning when it is cooler or on a day that isn't as hot. I would buy the food for the animals cause it is well worth it and maybe get an extra bag or two for your guests. The gift shop is neat and eating there is worth it too, just to get out of the car and relax and see the area is cool. It can be pricey, so you might want to see if you can get any coupons or special deals by asking them if there is any coupons or special days where it is cheaper. Fill up on gas before you go in, cause it is a long drive and you will need the gas. They recommend not opening your window all the way and that is good advice. We saw people there opening there window and sticking their head out the window, which isn't a smart idea. Bring your camera, as there will be many opportunities to take pictures. Good Luck on finding sleeping accomodations. You might ask Fossil Rim if they have any suggestions, maybe they might know of other places for you to stay.