I'll try to keep this as short as possible, but you have toddlers, so you know nothing about taking a toddler anywhere is ever short or simple
First and foremost, I'd reconsider the stroller. If you don't want to bring one on the plane, I highly recommend renting one when you get there. citystrollerrentals.com tends to be a favorite around the Disboards. They are somewhere in the neighborhood of $35+ per trip (it's a flat fee based on stroller and number of nights--for a single stroller for 3 nights, it's as low as $35). You can also rent strollers from Disney. What I like about City Stroller Rentals is that they deliver the stroller to your hotel (and other baby things, if you need them!) the day you arrive, and pick up on the day you leave, and you can take it outside of Disney, so on the way back to the hotel, you're not having to carry a million things (ie, diaper bag/backpack, 2 sleeping toddlers, anything you bought that day, etc). An average Disney day can be several miles of walking, in the heat... And not just 5-6 miles (10km); we've clocked over 13 miles (21k) in a day! That's a heck of a lot to ask a toddler/preschooler to manage, in my opinion. I'm a mom who wants to have what I could possibly need--I over-pack, I over-plan, I may occasionally over-stress

--so I'm not one that wants to figure out how to rent a stroller when my toddler is already upset and refusing to walk... or when my shoulders/back are too wiped out to carry them anymore!
Okay, now for the packing... I'll divide this into several categories, because I'd pack different things in different places, and buy some when I get to my destination. Thankfully, my youngest DD was very portable, even as an older toddler, so we went a lot of places
For the flight:
2 large backpacks
2 small backpacks
1 diaper, per child, per each hour you will be without direct access to your luggage, even if your 3yo is potty trained
1 large (80-count) pack of wipes per child
1 extra outfit, per child, per flight segment. 2 extras per flight segment if your kids are the runny-poo or pukey sort. 3 if they are anything like my kids

1 snack, per child, per hour of flight
3 new toys, per child, per flight segment
1 extra outfit for mom
1 extra outfit for dad
In the small backpacks, place: 1/2 of the allotted diapers for each child, the allotted outfits for each child, and the pack of wipes for each child. Let them each carry a backpack on their backs

They will think it's awesome (or at least my kids did/do!). We make a point to do a favorite character/animal for these backpacks to increase the exciting factor, and a lot of praise about being a big boy/girl for helping so well.
In the large backpacks, place: the rest of the diapers spread 1/2 and 1/2 in each bag, mom's outfit in one backpack, dad's outfit in the other backpack, snacks in each bag, toys in each bag. Use the rest of the backpacks for anything you may want easily available: your purse, travel itinerary, ID, boarding passes, iDevices/tablets/computers/etc.
Vons.com is the local delivery service. It's free delivery on your first order of $50 or more, I believe. They have a huge selection. From them, I would order:
2x the number of diapers you think you will need. Some toddler tummies don't like the change in typical diet.
1 large container of wipes per unpotty-trained child.
Pull-ups if you need them. (We don't use them except for traveling sometimes, but never will rely on them on a flight!)
Any snacky things your children will happily eat (goldfish, breakfast/granola bars, raisins, fruit, etc)
Any drink items your children must have (small container of milk, etc).
At the parks, I would take 1 backpack (ideally, in the stroller), with double the number of diapers you expect to need, the container of wipes, 2-3 extra outfits (is mine the only child who waits until she's cleaned up to have an explosive poo and ruin her clean clothes at the most inconvenient times?!?!), maybe an extra outfit for one parent (because DD never just got herself with her messes

), and several snacks to be pulled out while waiting in lines.
Favorite toddler spots in
Disneyland and California Adventure include: All of Fantasy Land (DL), all of Bug's Land (CA), Pirate's Lair (DL), the train (DL), the monorail (DL), the Main Street vehicles (horse-drawn bus, double-decker bus, fire engine, horseless carriages, DL), the Buena Vista trolley (CA), Ariel (CA), Buzz (DL), parades (Pixar in CA, Soundsational in DL), Redwood Challenge (CA)... Oh the list could go on and on and on.
If your kids get overstimulated, there's baby care centers that are nice and quiet, and will allow for some snuggling time

And, of course, you can always take a dip in the pool at HoJo too for a break from all the hustle-and-bustle!