My girls are 8 and 5, and I have been taking them to WDW w/o dh for several years now. We love Disney, and I am happy to share with you what has been a challenge for me and what has worked.
I find it easiest to
rent a stroller. Yes, normally my girls don't use strollers; but until very recently, I just found renting the double stroller the easiest way to go. I still carried everything -- snacks, wipes, pins/lanyards, autograph books, pens, etc. Hauling that bag on the bus and trying to hold the youngest's hand was enough. I knew I couldn't handle a stroller as well. Also, at the parks, there were times when I liked having them both in front of me when we manuevered through big crowds. I also liked that the stroller offered me a place to stash the aforementioned bag.
Meals could be a challenge as well. Again, trying to carry the bag, carry the tray of food, keep up with the kiddos. (My oldest is very good about sticking close. My youngest is a wanderer though.) Also, I wasn't comfortable leaving them at a table to save a place or something like that while I went to order. My girls lik the Mickey waffles, so we would have breakfast at the food court before we left. I found the food courts at the resorts much easier to manage than the CS places in the parks. I'd bring snacks, and we would often have a late lunch. After the lunch crowds died down, it was much easier to order our food. We'll stake out a spot and eat while we wait for the parade. If it was a late night at the park, we'd just snack. If we were in our room, they love to get pizza.
The rides were also a challenge for us. They just had to accept that if we couldn't all ride, then we couldn't ride. I also told them that I would not force either of them to ride something they didn't want to ride. Some rides I was comfortable letting my then 7 yo sit by herself, and my youngest and I would be right behind her -- like Buzz Lightyear. My girls also learned to compromise. My youngest would occassionally agree to ride Splash Mountain if my oldest would agree to do Stitch's Great Escape. However, when they couldn't reach an agreement, we couldn't ride. Like I said, I didn't force either of them to go on a ride they didn't want to(or were too frightened to do). Sometimes that meant they missed out on their favorites, but that's just the way it goes sometimes. (We live about 90 miles away and go often, so missing out ona favorite ride isn't too big a deal.)
Restroom breaks. The companion restrooms are great, but we don't always use them. My girls go into their stalls and stay there until I come get them. Yes, it means they are in there a little longer, but I prefer that to them leaving the stall themselves and washing their hands and such while I'm still in a stall. There has been a few discusions about boys going into the women's restroom and how old is too old. I think this method works great for the moms with boys. If they are in a stall, they probably aren't making anyone uncomfortable. Although personally, I don't think a 5 yo boy is too old to be in a women's restroom but is too young to be left outside one on his own and I wouldn't feel comfortable sending him into a men's room alone either.
Those are really the biggest issues I've had with having 2 children that age and not having another adult along, and they really aren't a big deal. We go all the time, so it hasn't deterred us at all.
Go and have a great time. Your 2 oldest will enjoy having your full attention for a bit, and it'll be fun fr all of you. I'm sure.
. At first I was a little unsure as to what I was putting myself in, but I got a hold of my nerves and started planning. I think just having patience, organization and a lot of rest time and just have FUN! 
We have had no prob at all, we always carry a backpack(hands free) and always 
