Priceline only guarantees a room for 2 adults. But I have heard some people say on this site, that pretty much all Orlando hotels cater to families and 4 to a room is quite standard. You shouldn't have any trouble getting 2 double beds (but as I said, no guarantee). You may have to pay for extra people though, through the hotel, I'm not sure. You could call some of the hotels that priceline uses and ask if there would be an additional charge for this. Or maybe someone here can answer this. Great deals are definitely out there at priceline - I got Wyndham Orlando for 14 days in July for $30/night (plus AMX bonus $20/night which is now expired)
GOOD LUCK!!