I'm assuming by cabins you mean the Grant Grove Cabins? I've never stayed in them personally so can't say for sure one way or the other, but during the month of October our average overnight low is 38 degrees, so definitely bring some warm clothes for the evenings.

I always say you could easily spend a week in the parks, but two nights is generally enough time to see the major points of interest. It takes roughly 45 minutes from either park entrance to reach Giant Forest, so many people do prefer to stay inside the park rather than making the commute each way.