I don't think you can cover all the sites in a day, much less 2 hours. Also, at least as far as the Roosevelt properties are concerned, you have to take the National Parks van to the two cottages, and it has a schedule, so can 't just go to them whenever you want (for example, if you have a car). Actually, you can also get to the Vanderbilt mansion in the van, don't know if they allow you to drive there (can't drive to the outlying Roosevelt properties).
When I was up there I took the NPS van from the Poughkeepsie train station and on the way the ranger explained the set up and how you had to plan how you were going to do it because van schedule didn't permit seeing all in one day.
I would skip Viator. They will sell tickets wherever they can, but probably know little about what they sell..
In my experience, there are not mobs of people up there trying to get in, like, say, at some of the museums in NYC. So I don't think there is any point in buying something with "guaranteed" access. Just read the NPS website page for these properties and see if that will work for you.