I have bid with priceline before and I know they don't guarantee 2 beds, but I have called the hotels direct before and put in a request for what I needed. Most of the time they are pretty accomidating.
The best site for information about using Priceline is www.biddingfortravel.com. Read this site carefully and you should get all the info you need. I have used Priceline many times for the US and Europe and I have usually been delighted with the hotels I've won. Be aware that you can't chose a specific hotel but by being informed you can often land a particular hotel.