Hi Judita,
Are you arriving by plane on Sunday?
The unfortunate thing with
Navigo passes is that they aren't valid until Monday morning. So, if you're arriving by CDG on Sunday, you'll need to buy a single billet Ile-de-France ticket for you and each of your party to get from CDG into Paris, in addition to the Navigo for the week. The tickets will be €8,40 for adults, €5,90 for kids
10 and under.
Either way, I think the Pass Navigo Découverte, 5 zone (covers EuroDisney & CDG, both in Zone 5, and Versailles in Zone 4) is the best option for you guys. It'll be €33/each for the week for 5 zones. Don't forget to bring 3cm x 2.5cm photos (or even photocopies of headshot photos) for the cards.
You can use the first Sunday as a decompression day, stroll around the hotel/local area, then the next day go crazy with the sightseeing all over using the pass navigo. You'll love it. It's so easy to use and so convenient.
I do recommend taking the bus around Paris when you can. You see a lot more than on the metro, although their routes are very difficult to understand. Taking the bus is best when you're randomly sightseeing, rather than having a particular place you want to get to in the quickest time possible.