Hi Rathi,
The
Passe Navigo Découverte, loaded with
5 zones, purchasable at
CDG Airport, is your best Paris Metro/RER ticket solution. It's important that you get 5 zones for your pass as you plan on going to Versailles (Zone 4), Disneyland (Zone 5), and back to CDG airport (Zone 5).
For your first day, arriving on Sunday, you will have to purchase individual tickets to get from
CDG Airport to Paris as the Pass Navigo only works starting from Monday onwards. These tickets are known as
Billet Ile-de-France and are purchasable at the Airport ticket windows (or
ticket vending machines if you have a smart-chip credit card). Each ticket will be 8,40€. One per adult. Children 10 and under can use reduced fare tickets at 5,90€ each.
If you have plenty of luggage and wish to avoid any stairs in Paris Metro or RER stations, consider taking the
Roissybus or Les Cars Air France coach instead. These buses only stop at certain locations within Paris, such as Opéra, Arc de Triomphe (Etoile), and Montparnasse, but if that's your destination, it works out well.
Best regards,
Ben