A lot just depends on your children, their sizes, personalities, where u are staying, cost, whether u want to wait in line to rent everytime u go to the park. During our stay April 16-24, I never saw anyone on the buses with a tandem double, only umbrella doubles, one double jogging stroller(which was HUGE), and several singles. So I can not tell you how easy it will or will not be. My Graco tandem does not fold up easily, and is very heavy. I am assuming that dh will be handling stroller/diaper bag while u handle the 2 little ones. This is what we did.
I am 7 mnths pg with a 4.5 yr old and 22 mnth old. We bought 2 Maclaren Triumphs(
www.allbeebaby.com has good prices, but we bought ours from Babierus). The 2 singles were much easier to handle in the crowds and on the bus. At the resort, the youngest rode in the stroller and the older enjoyed the walks. We have never had a problem with the two "having" to do what the other does. It was nice to have the option of dh and I taking a child and going different places.
We bought the stroller connectors to use if I was left with both but never used them bc the Macs are soooo easy to steer. I can't go back to Graco again. I just steered both or had oldest push hers to the bench or table where we waited. Dh and I often steered with one hand and held a food tray in the food court with the strollers. No way with Gracos.
The triumphs have a sunshade, a wonderful raincover that we used 1 day with no leakage just a little fussing from youngest(but he was dry and happy after the shower), a small basket, a carrying strap, easy/quick fold, and is fairly light and compact.
Oh, the Macs were the only ones that fit my very petite 4.5 yr old comfortably. She is only 40 lbs and 41 in, so not huge. we almost bought the combi savvy but when we tried it out at BRU then it did not fit her hips.
If u have no choice but the Graco, I would drive your vehicle or rent. Staying onsite, you will get free parking, no wait for buses, and less hassle/stress.