Wedding advise.

So this will be long and I apologize but I'd really like some advice. I'm getting married this year yay! But so is my step sister (we don't really talk and never have actually been a huge part in each others lives. She lived with her dad and hates my side of the family.) Anyways, I wanted to do a cruise wedding because we found an awesome Disney cruise deal!!! And it's been a dream to not only go on a cruise but a Disney one, I'm a huge Disney fan. I'm pregnant and due in May. Well if you go on this cruise line the baby has to be 6+ months making the wedding for November or December. I'm totally okay with that except for my step sister chose the end of November (which I've had picked out for years!!!!) My step mom messaged me saying how rude it was to steal her daughters thunder and plan my wedding over hers. And how I am already going to be the first one to have a kid and to let her have her moment. And that if I planned mine around this time she would not attend. Then continues to freak out because my side of the family said they would rather attend my wedding (like I said my step sister really has no relationship with us). I'm super bummed because Now it's people choosing sides. Who likes who more. The only other option is for me to wait till next fall or winter to get married or do it the following summer which I really don't want a summer wedding. I want to be married. And I feel like I'm being put on the back burner by my step sister and mom. How can I win? Has anyone else ever been through this?

Edit: because this would be a four day cruise it would be more logical to do it the end of November or December due to the holidays. People are able to take off. Not that I'm claiming a month or anything. So doing it January or October family and friends would not be as likely to take off or attend. The only time we could get his family and most of my family at the same time is unfortunately during those times.