I would drive BTH and keep that night. You should be able to score something at Old Faithful. Take the first one you can get, lodge, inn, cabin, etc. Then maybe you'll get lucky and get the one you actually want later. Sounds like you've made good progress, even if nothing else becomes available.

For me Mammoth is the least interesing spot(certainly worth a bit of time though). Geyser Basin around Old Faithful-I could spend several days there just geyser gazing.

I think the general opinion would be that Mammoth isn't what it used to be and I would try to drop that.

Call every day or more often and try for OF. I really like the location of Canyon. Close to the big falls and near wildlife. Tower might also be a good area.

When you get OF that might eliminate Lake as they're not too far.

Are you planning anything for Grand Tetons. It's a beautiful place. I would try for Signal Mountain.

Call, call, call. The problem is that most tours and people release their unwanted rooms in the last month. So it might look bleak until suddenly you get what you need.

Yellowstone is a very big park and you might not want to be driving at night due to wildlife.

Thanks. Not planning anything for GT. It is our first trip to YNP and can't do everything especially with a 7 and 9 year old.
Wondering if I should cancel the Silver Gate night and just drive to Roosevelt. I'm estimating an hour and a 1/2 to get from the NE entrance to Roosevelt which would equal a full day of driving from Billings area.....have to think that one over. Somebody trashed the Pine Edge cabins in Silver Gate so I am having second thoughts there. Might pick a place about an hour away from Billings airport to cut down on the drive the next day.....

I wouldn't cancel anything, until you had more nights somewhere else. We really really liked staying at Lake, so I don't think I would eliminate that night. Mammoth might not be a bad thing to stay at, I just wouldn't spend the entire day right in that area. It certainly could be somewhere you end up at though. Since you are there in August, you might spend part of that day soaking in the Boiling River(which is near Gardiner).