Are there any ski lodges for your family?
In stead of staying in the city like Salzburg, you had better stay at the lodges near the ski area where you are going, especially such big group.
Usually, they have different type of rooms for couple and family.
Commute between ski area such as Kitzbuhel and city is quite a hussle for big family.

I have stayed at Sheraton Salzburg and I don't remember they have two double beds or two single beds. Anyway, I don't think there is a space for two rollaway beds in the room although the room was not that small.