Hi Melissa!
Thank you for bringing your question to the Disney Parks Moms Panel!
I looked up the Joovy Big Caboose stroller because I am not familiar with it. I did see that the dimensions of that stroller are a bit larger than the
Walt Disney World website's list of prohibited items allows. It seems that it is longer than allowed, but not wider. Do I think you would be able to take that stroller into the park? Probably. But, it is important to note that Disney Security has the right to not allow it to enter, so that would be a slight risk.
There are single and double stroller rental options at each theme park and Disney Springs, as well as companies that you can rent strollers from for the entirety of your vacation. You can find information and links to details about rental companies
here at this Walt Disney World stroller rental link.
I'm sorry I don't have a definitive answer for you. Like you, I sometimes see things in the parks that are technically against the rules. I don't want to tell you that you would for sure be allowed to take it in, when it's possible that you wouldn't.
It looks like your trip will be here very soon! Have a magical vacation and please let me know if you have any other questions.