My husband and I got a magical upgrade to one of their Junior Suites on our last trip there. It was very spacious! Basically, a Studio and regular room with the lockout removed, so you get double of everything. Two Full baths, two TVs, two minifridges, etc. and a whole bunch of storage space. The Studio side would of course have a foldout bed. If that is not a bother, than the Junior Suite is a great option. I haven’t been there with a baby, but imagine it would work really well if your sister and baby shared the one side of the lockout. My husband would stay up later than me at night, and I couldn’t hear the tv on the other side with the door shut. Hope that helps!