If you dont take one, remember you will have to slow your pace way down. Since my daughter is no longer stroller age, even though Im pushing my son in one, we slow way down so she doesnt tire. Your ticker says 7 months, so it wont be as hot and that will help. In October we took a short trip and my daughter was able to do 30 theme park hours in 3 days because we moved at a slow pace. Not sure how many days you are going for, but even if you slow down, it might not be the first 2 or 3 days, but days 4 onward where you might see some issues. Or in a larger park like Epcot or a hotter park like AK.
I like the suggestion another poster had of taking the single for the 2 year-old, but let it be a stroller your 5 year-old can use if need be.
Our trip coming up is in June, I booked for the maximum days I could afford and mixed in half days where we only tour until 2 or so.
Really it is about what will work for your family. On our first trip, I pushed my dd (then 7) around for a couple of days after she had some tummy issues. She still wanted to go out, but wasnt really up to walking. She was under the weight limit for the stroller we had so I wore ds and pushed her. I probably looked like a pack mule and several people commented on how loaded down I looked. I didnt care. It was worth it not to have to sit in the room until she was back at full strength.