As Michael said, UT sells actual Disney tickets, at a discount. I have used them for many trips and never had an issue. A couple of things to remember when ordering from UT:
First
remember that the UT prices posted INCLUDE tax; the prices on Disneys website don't have tax included.
Second
They will ask you when you need your tickets by. This is totally irrelevant regarding the ticket- they won't put a date on them or anything- but although they say they'll ship in 10-15 business days, sometimes they use this to prioritize the shipping. You want to make sure that you have your tickets in time to link them to your
MDE account so you can make your FP+ reservations. I usually give them a date that's about a month away from the date that I am placing the order on.
I'd order an 8 day ticket, or even a 7 day if you need to save money. You have water parks and hopping, so you'll have PLENTY to do to keep you busy. In addition to theme park entry, you'll have multiple days of water park entry, Disney Quest, Downtown Disney, etc., as well as being able to go to outlets if you have a car. No worries about enough to do
so I'd order from UT, too, to save some extra cash.