Here's my two cents. Three tiny kids is tough. Definitely work. I'm not discouraging you - I'd do it in a heartbeat, just be prepared to work hard!
We went with an 18 month old and I was 5 months pregnant. We rented a stroller and it was a piece of cake. We went again with a 2 1/2 year old and an 8 month old, we used our double stroller (Combi - folds very small & is very light weight) and that was smooth sailing!
We went again with a 4 year old, 2 year old and an 8 month old -- and it was much harder. We used 2 strollers (single and double) when my parents were with us for a few days, and one double stroller when it was just the two of us with the kids. We would rent a single for my 4 year old at the parks but had her manage without the stroller to and from the parks.
With the stroller one of us would take the stroller and one child and the other would take two kids -- or all three -- to get on and off the bus. DH would take the stroller and I would take the kids most of the time. Getting on and off the bus is owrk for little ones because the steps are steep. Little ones need to be carried.
Quite honestly this felt like a lot of work on that trip -- and if I were doing it again, I would opt for a hotel that had a boat or monorail to one or more of the parks so that I could just roll the stroller on - at least some - not having to get the kids out, fold it up carry it on., etc.... And at the very least, if you are using bus services all the time, I would at least consider just bringing the double and renting a single so that you don't have to deal with two strollers on the bus all the time.
The biggest draw back in renting (aside from the added expense), is getting to and from the bus stop to the hotel room or from the park to the bus if the 4 year old is very tired, but some of the time the 2 year olds can be inthe double stroller with one parent and the other parent can manage witht he older child (carrying sometimes, if s/he isn't too heavy).
Hope that helps! Like I said, I would do it again in a minute, so I'm not trying to sound too down about it, but my DH and I did work on that vacation! LOL