Howdy again Lorna and thanks for your follow up question!!
Disney's Old Key West Resort is a great choice for you and your daughters!! Old Key West can sleep up to 5 and has 1 king-size bed, 1 queen-size sleeper sofa and 1 sleeper chair. The sleeper chair is similar in size to a twin size bed.
Old Key West and Disney's Saratoga Springs Resort and Spa are both located a short boat ride away from the great shopping, dining and entertainment that you will find at Downtown Disney. Both are Disney Vacation Club Resorts and offer many of the amenities of home combined with the magic of Disney.
Given that you are looking for the additional bed, Old Key West is a perfect choice. It's a very relaxed resort and given that you will be at Walt Disney World for an extended period of time, I think you will find it to be a perfect home away from home for you and your girls.
In your 1-bedroom villa, you have a spacious living room and fully equipped kitchen as well as a full size washer and dryer. You can stroll around the resort or enjoy some time pool-side. Saratoga Springs does have a Spa but if you need some Spa time while you are staying at Old Key West, you can easily make your way to Saratoga Springs.
I love both resorts and have stayed at both many times. Both are fabulous and I think you would love staying at either. Saratoga Springs is a bit newer but there is nothing like a classic and Old Key West was the first Disney Vacation Club Resort built. If we were planning to stay as long as you are, we would, most like, have Old Key West on the top of our list.
I hope this will help you in your planning. Please let me know if you need any further information. Thanks again for your questions and have a magical day!!