First, take a deep breath. Vacation planning with a group can be chaotic with a wedding thrown into the mix!
Realize that you will have to sacrifice something here. As much as any of us want to have it all, we can't. (Not until at least there are teleporters and even then...)
There are a lot of factors your post didn't include such as if money had been put down, can any be saved or transferred your overall budget - not that I expect you to share this, just for your personal consideration - what everyone in the family wishes - again knowing you can't have everything - etc.
Firstly has money been put down on either trip? Can you get it reclaimed or moved? Is it worth the monrtary loss (if rescheduling is going to cause you to lose out on the trip).
Since the wedding is a must, let's address the vacation. Assuming you very much still want to make it work (regardless of payment), I would opt to drive to the wedding, fly from wedding to Orlando's airport, take the shuttle and go to the ship.
I've had my DD at the park when I was nursing. I've had my DS on a cruise as a toddler. While both vacations have their own fun memories, I think as a parent you would enjoy it more on the ship.
Also, while Mickey's Christmas party *is* worth it at least once, it is better when kiddo is older to enjoy it. (We took DS and DD in 2014, and while they did have fun, it would have been better for them if they were a bit older.)
And here again, Hollywood studios and Animal Kingdom are going through a lot of construction. It would be better to go later once kiddo is older and so many new adventures are ready!
So if it were me, and I absolutely had to make this wedding: I would drive up (rental cars are surprisingly cheap for such excursions) and then fly down. Or in a financial pinch, drive both ways. But definitely forgo your land portion of the land and sea vacation. Just go on the cruise and enjoy it.
I wish you and your family the best of luck!