Please note that just because a lift/elevator is in the hotel description, it doesn’t mean the lift goes to every floor. Or that stairs aren’t required just to get INTO the hotel. If this is an issue, be sure to contact the hotel and ask specifically about stairs. Especially in older hotels.
We did a lot of searching for adjoining rooms and found that they are available. On booking.com, search for two rooms for 4 people, and in the filter mark Elevator. You then need to look through the results for Adjoining Rooms. I wish there was a filter for that.
I almost booked Hotel Residence des Artes for our group of 4, but ended up booking an apartment. It might suit your group. It’s very central, close to metro and RER lines and taxis.
The sites you mention are very spread out, so no hotel will be central to them all. Just be ready to take taxis. I would be looking for a neighborhood that has lots to offer in itself. Then decide do you want a modern feel, or old world feel with modern conveniences. Prepare for rooms (and bathrooms) to be VERY small. Look at pictures very carefully, and note room sizes. Read reviews carefully. I found 110/115 sq feet very common.
Google Earth is great for getting a “feel” for a neighborhood.