We are 4 people arriving Friday 1 April, staying till Fri 8 April.
We will visit Valle d'Europe Monday and EuroDisney Wednesday. Which ticket is best?
What shall we take from CDG airport to ChampsElysee on Friday?
Since most of your travel is happening during the week, it would still be worth it to purchase a Navigo Decouverte pass when you arrive on Friday (even though you cannot use it till Monday).
For your initial travel to from CDG to Champs-Elysees you could purchase single-use RER tickets (total cost 40€) and take the RER B from CDG to Paris Chatelet les Halles, transfer to RER A direction Cergy le Haut / Poissy / Saint-Germain-en-Laye (either of the three) until Charles de Gaulle Etoile station (at Arc de Triomphe), then it's a 10 minute walk down Champes-Elysees to George V. An alternate which does not require as much walking from Arc de Triomphe to George V on the street, but requires a fair amount of walking at Chatelet les Halles station, you could transfer from RER B to Metro Line 1 direction La Defense until Metro station George V. Please keep in mind that although the RER to Metro transfer sounds more direct than RER B to RER A, it's more complicated within the cavernous Chatelet les Halles station to transfer from RER B to Metro 1, than RER B to RER A. If you keep your eyes on signs for Metro 1 (yellow colour) within Chatelet les Halles, you'll eventually find the platform.
Another option you may consider is simply taking a taxi from CDG to George V since you are four people with luggage, the 60€ price (approximate) may be worth the extra cost. It would also likely be faster unless you are traveling within rush hour.