Point me in the right direction, s'il vous plaît.

Even on an early Monday, I'd give it 45 minutes drive to the airport. All in all, recommend leaving at 5 am. Reserve a taxi pick up ahead of time. Take it from one who has already missed a flight there.

A taxi is very little more for 5 people than taking the train. The train will cost you about 52 Euro and you will be hauling baggage up and down stairs at transfers. A cab will be 59 plus 7 to book ahead which you need to do in order to get a large enough cab at the crack of dawn. Make clear when you reserve on the G7 English line that there are 5 of you and luggage and they will send a van cab.

I can't help with getting you to the airport, but I would like to ask how you arrived at flying rather than taking the train (Eurostar)? Are you going somewhere in the UK other than London?

Flying into Birmingham (for some family history) driving down through Wales, Bath and then to London. We are taking the Eurostar back to Paris for our flight back to the US. Cost was about the same when I bought the tickets and flying is saving us some time.

Are you aware of the excellent local history department at the Birmingham Public Library? They have all sorts of maps, census information, newspapers on microfilm, commercial directories, and very helpful staff...... They are a gem.

How many people are involved?
Just go to the regular taxi stand at CDG and stand in line. The agents will give you the car size you need if you have more than 5 people.
Flat rates are in effect - you will pay 50 EU - plus 4 EU if there are any more than 4 people. No luggage fees.
When you are ready to leave Paris, use this reputable website. There is a 7 EU reservation charge for the convenience. Same flat fee - 50 EU. If you have extra passengers, you will pay 4 EU each plus the 7 EU convenience charge.
https://www.g7.fr/en/

Uber cannot pick up passengers at CDG.

Nigel, good information to have. Thank you! Can you tell me how early we need to be to the train station for our return on the Eurostar?

Chexbres, thank you for the website!

54 euros from the 16th (50 euro flat fee from the Left Bank plus 4 euros for the 5th person) to CDG plus the 7 euro reservation fee. 61 euros for the taxi.

With five people to wrangle around the airport, I'd aim to be there for 6:00.

Eurostar check in at London? I'd allow an absolute minimum 45 minutes, probably closer to an hour.

From Gare du Nord to London? At least an hour. I spoke to somebody yesterday who said they were there an hour ahead and barely made it, and some in their queue didn't.

Re Eurostar. You MUST be at the ticket barrier at London St Pancras at least 30 minutes before departure. This is because after the ticket barrier they do a security check, and you go through passport control twice (once to exit UK, and once to enter France). At Paris Gare du Nord you just walk off the train.

If you have not been there before, I would aim to be arriving at the station 45-60 minutes before departure, as you need to find your way to the correct part of the station.

Additionally, our flight leaves on a Monday morning at 8:00 AirFrance
Terminal 2E. AirFrance website says the check-in deadline is 40
minutes before the flight (we will plan to check-in online, we are
travelling with carry-on only) and boarding deadline is 20 minutes
before the flight time. I am not sure how long it will take to go
through security. Will arriving at 6:30ish be early enough?

You might want to arrive by 6:15 just to be on the safe side regarding security lines.

I was just in London.
Leave your hotel at least 60 minutes ahead of time to get to Saint Pancras.
There is a mall there, where you can do whatever you want to do.

You will only be allowed to board 30 minutes before your train departs, but people take a lot of time putting things into bins, etc.
Then, you go through British Passport Control, which may take a lot of time - I was there an hour, and the line did not budge.
Then, airline Security, then French Passport Control, which takes maybe 15 minutes.

Once you're safely in the lounge, you have only 30 minutes to board your train, so get in line and watch for your train number.
Hopefully, you will be packing lightly, and can put your luggage above your seat.
Never leave your gadgets or purse unattended.