Party of 4 will be arriving at CDG (Terminal 2) on a Sunday morning and then in the afternoon we will be taking the Eurostar from Gare du Nord to London. We will be returning to Paris via Eurostar on Tuesday evening and staying in Paris until Sunday. While in Paris we will be taking the RER to/from Disneyland one day and the RER back to CDG. Based on your amazing advice on this site, we plan on purchasing single-ride RER tickets for Sunday (for CDG to Gare du Nord), and then purchasing Navigo Decouverte Week Passes for our time back in Paris (Tuesday- Sunday).
QUESTION- Which would be easier for us? (keeping in mind that we speak very little French)
1) Purchasing the Navigo Decouverte Week Pass at CDG on Sunday upon arrival?
2) Purchasing the Navigo Decouverte Pass at Gare du Nord on Tuesday evening when we return from London?
Which location is more convenient/easier to purchase Navigo Decouverte Passes? If possible we want to avoid long lines, but we are also concerned about communicating in our limited French that what we want to purchase.
CDG Train station ticket offices are the easiest place to buy Navigo Decouverte week cards. They're pretty much guaranteed to never run out of blank cards, the ticket staff all seem to speak English nowadays and it's difficult to miss the ticket offices. Not the case at Gare du Nord which is also a zoo at most times of the day/early evening.
I highly recommend making the purchase at CDG upon arrival for both the single-use RER tickets for Sunday and the Navigo cards for use later in the week. There's no benefit to waiting to make the Navigo purchase and you would have to line up a second time if you did so.
Hope you have a great trip to Paris & London.