CDG to Tour Eiffel Area Questions

1. I once saw a video of a person traveling from CDG to the Eiffel Tower -- I do not have a link but if you search in Youtube for easiest way to from Charles de Gaulle at the Eiffel Tower, I bet it will show up. What I remember most about it is that easiest was all caps and that the guy kept forgetting the name of the Champ de Mars station and got a little confused because he did not see Champ de Mars on the signage. In any event, you just follow the signs for Line C and go up the escalator to the platform. It's a long escalator because the RER B is pretty far underground and the RER C is just below the surface.
2. You cannot order a Navigo card for delivery to the U.S.
3. Just take the first available train but if you want an express train, check the four-letter mission code displayed on the train and platform screens. Codes starting with letters like "K" or "J" for trains heading to Paris are generally express.

I suggest you download the City Mapper app it is very helpful plotting out the most efficient routes and telling you which platform you need to be on and precisely which exit (sortie) to take. The RER and metro have good signage to direct you where you need to go, and you'll have to use an escalator or elevator. Make sure you scan your pass on entry to the station (and scan out for RER trains). Pay attention to the maps in the stations to make sure you board going the right direction, and each train also has a sign that lights up showing where it is on the route. Worst case you hop off if you're going wrong direction and slide over to the correct platform. There are many YouTube videos about using the RER and metro in Paris. Here is just one of many: https://www.youtube.com/watch?v=WxByaG0s-Uw

AFAIK you can't get the Decouverte mailed to you as it requires a photo (remember to bring a passport sized one for each of you). Unless it is travel mayhem at the airport I can't imagine you'll suck up 2 hours waiting at the IDF office. I had to use a staffed window in a very busy metro station and I waited 5 minutes max.

Will you all have smart phones with you? If so, you can download the IDF Mobilités app set up an account and add a Navigo Découverte card while you are waiting for your luggage and use your phone as your ticket and you will not need a photo. I know that some people prefer the physical card but I have never had any problems with my virtual tickets.

I see you changed your question. Re: revised question 1, there are no luggage restrictions but if the escalator is out at Notre Dame St. Michel station, you could have a challenge. Otherwise, if you can manage your luggage and secure your items to keep yourself pickpocket, the trip should be okay. I don’t know your budget but you may want to consider a taxi for 65€. Will you be arriving directly from the US? If so jet lag + first trip to Paris + a change of trains to reach your destination + a 10-minute walk = taxi in my book.

1. You do not need a Navigo Découverte, which is only a card, if you use either the IDF Mobilités app or the Bonjour RATP app and setup an account. If you want to load a Navigo weekly pass, at 31.60€, you need a photo either way but using the app lets you take a selfie and add that to the account on your phone. Some phones, later Samsung and Apple models, have the NFC circuitry builtin and you can keep them in your purse or bag and just wave that over the reader. An app does not need to be active on these models.

2. Some RER B trains make fewer stops than others, but the train arriving the quickest will always be the next train, no matter how many stops it makes. Express trains never pass other trains. You can waste a lot of time waiting for an "express" train.

Note: unless you arrive on a Sunday morning, or during August, inbound traffic from CDG can be brutally slow, taking up to 90 minutes to reach the Left Bank. If you can easily handle your luggage, the train will be half that time and the fare will be included in the Navigo pass you are purchasing.

Découverte cards are only sold in the Ile de France. The apps (specifically setting up accounts) can be geoblocked from downloading in some locations outside France.