Hi there Renai or should I say g'day, mate!
Boy, I wish I had your problem... I would love to be in Walt Disney World for 17 days! The reason you don't see the tickets for more than ten days is because after a certain amount of days, an annual pass is more economical than buying the individual tickets.
I would buy the annual passes and then use your pass holder discounts to try to secure a lower rate for your resort stay. Here is a
link to all of the benefits of being an annual pass holder. As you can see it does provide some great benefits over the standard Magic Your Way (MYW) Tickets.
Another option would be to purchase an 8 day MYW ticket with the Park Hopper and
Water Park Fun and More options. This would give you 16 days of play in the Walt Disney World Resort including Blizzard Beach, Typhoon Lagoon, DisneyQuest® Indoor Interactive Theme Park, ESPN Wide World of Sport Complex or a round of golf at Disney's Oak Trail Golf Course. You can use the park hopper feature in the four main parks for eight days and in between those days go to a water park or play golf. It's a great option.
I know this is a lot of information to take in so if you have any questions just let me know! I hope this helps with planning your trip to Walt Disney World seriously, we are always here to help! Thanks for asking the Moms Panel and have a Magical Day!