Trying to make this work on points without added expense.. Looking at La Defense , Champs Elysses in Paris and St Pancras and County Hall in London.
I noticed River Gauche is available Cat 7 for lower points. Does this location have a CL? Is it close to the subway station/ Trafalgar Sq.
I think the issue you are going to run into is that while standard rooms may be King/2 Doubles, most suites/junior suites/etc. are just a king. So while it is a bigger room, there's not going to be places for 4 adults to sleep.
Are you really sure you want 4 adults in a room? That does not sound like a vacation to me.
The Rive Gauche is very conveniently located for the subway and for the RER. (the later for trains to Versaille, the airport and alike). It has a very nice CL serving tasty morsels and a has a very helpful and friendly staff. If the weather is nice, it is a delightful 30 minute walk to Notre Dame and the heart of the tourist part of Paris. Unless you are upgraded to a much larger room than the one I was given, four adults in one room is not likely to be very comfortable or practical.
I've stayed at the CE property and there is no way to get four people into a standard room, and they won't allow it. The last time I took the family I had to purchase an upgrade to a larger room, which was quite comfortable for the four of us. As far as securing a free upgrade beforehand, good luck with that.
For central London the only hotels that offer double doubles for redemption are the Park Lane and Marble Arch Marriotts. PL is a cat9, MA a cat8. Cash rates for PL are typically 50% more than MA suggesting PL represents better redemption. Both have exec lounges, though I remember reading somewhere that PL was the better. Location wise, there's little to choose. Ironically PL is right next to Marble Arch, but the Marble Arch hotel is a few minutes walk from the location with far less salubrious surroundings than Park Lane! That's as far as I can go here as I've stayed in neither, though been to both for meetings...
The only Marriott's in central Paris that offer double doubles are 2 Renaissance's, Arc de Triomphe & Parc Trocadero and the Marriott Rive Gauche, which despite the website isn't super-central to anything, unlike the first 2! I can't comment for the 2 Rens but I have stayed at the Rive Gauche, it's very easy to reach from CDG (RER to Denfert Rocherau, as you emerge from Denfert follow the road signposted Place D'Italie, the hotel is a 5/7 min walk on your right). Its lighter on your points as a cat7 and has a good exec lounge.