Hey howdy hey Julie and welcome to planDisney!
Sounds like your next trip to Walt Disney World Resort is going to be a great time with so much spent in the parks. The fall in Walt Disney World is such a great time to visit the parks. I love the fall decor down Main Street, U.S.A. as well as the
Disney After Hours Boo Bash in Magic Kingdom. One of my favorite things to do in the fall, however, is to visit
EPCOT International Food and Wine Festival. It is such a great celebration of so many great food and drink offerings. I never do have enough days in the park to visit every booth I planned on!
Now as far as visiting the
Theme Parks, you have found out that Disney only sells 10-day Theme Park tickets as a maximum amount. What you would need to do, is to break up the days. So you could buy 10-day park tickets for your party and then a separate transaction of the three-day tickets to get the 13 days in the parks.
Another thing to keep in mind going forward, since your trip is not until October, you can buy your tickets now and then keep an eye out for
Annual Passes. The sale of new passes is currently paused, but when they do come back, you might have a more economical option buying an annual pass rather than 13-day park tickets. Annual passes do come with perks such as discounts on food and merchandise in the parks as well as special Passholder events. Tickets can always be upgraded to an Annual Pass so it's worth keeping an eye out for to see if it fits your budget and needs going forward.
Good luck with the continued planning of your trip in October. We cannot wait to welcome you to the Most Magical Place on Earth!
Happy planning,
Nick