First of all, WELCOME to Flyertalk.

You've got some conflicting requirements to say the least.

Your best bet would be the Georges V. If you go to the bar late in the afternoon, early evening, you might be able to do some celebrity spotting, but please don't gawk. Although many of the patrons although famous might mean nothing to an American.

Most of the hotels you are mentioning do not have very large rooms by American standards.
The idea of a third bed in a room is strange to me because your children are already too old in my opinion and besides you are not going on a camping trip but in some of the most luxurious hotels in Europe. Rates ARE going to be high, so $ 1'500.- is about right.

All the hotels are a little snob, they are five stars.

At such short notice, I doubt you'll get a room though.

2nd choice would be the Crillon, 3rd the Meurice.

Prince de Galles, Bristol cater to an older generation, very discreet, many celebrities but the kind that avoids all type of contact and usually cannot even be seen entering and leaving.

The Georges V is the most lively and might best meet your requirements but hurry up for reservations.

By the way, the end of July is not ideal, you'll meet more Americans and other tourists than celebrities. Most are on the Côte d'Azur or in Italy or in the Greek Islands.

Have a good stay and if you need more specifics, drop me a PM.