In true Commando spirit, I like to open the park and close the park. But, we only do one park a day.
Never had twins, but we went when my children were 18 months and 3. I got PH once, and then never again. Just like you said, the reason was because we lost so much transportation time. And, it's just not transportation from theme park to theme park, but transportation from wherever you are in the first theme park, out of the theme park, walk to the bus stop, wait for the bus, then bus time, then walk from the bus stop to the new theme park, and then into the new theme park.
With the young ens, if the adults are interested in riding the bigger rides, you can walk over and do the parent exchange thing. We just enjoyed going slow and doing the rides they wanted, then back to the resort for a nap in the heat of the day, and then back for more fun. Then, we stopped going back for naps and youngest would sleep in stroller and oldest would sleep on me, and we would find the AC cold indoor for naps. France movie was a favorite nap place. Then we stopped stroller when youngest was 5.
You'll get different opinions and everyone knows their children best. So, ultimately do what you think is best and have fun with your family, and everything will be fine.