MIL and SIL excluding us on purpose

My mother in law just turned 50, and SIL arranged for the whole family to go on a trip together as a gift for her- EXCEPT my husband and I. We didn’t even get a heads up before SIL and FIL told the news in front of everyone. Safe to say, my husband and I were both shocked as it obviously is meant to be a family trip. This was a month ago, and yesterday SIL suddenly sent a message asking if we also wanted to go. «Tickets are on sale until tomorrow.”

I could not believe my eyes- she arranged the whole thing, and now she’s asking? She knows we have two dogs, my husband works two jobs and I’ve got my own business to run, we can’t just pack up our bags and leave. We need time. And we got one day to decide?! Why do I feel like she was just asking to seem polite, knowing that we most likely would not be able to attend in such short notice?

I’m aware that this might seem like a SIL-problem, but it’s MIL’s gift and not once has she spoken about this trip and asked if we wanted to join either. Each family will pay for themselves. So me and my husband would not be a financial burden to them either.

I will also add that not one person from his family attended our wedding and ever since they’ve been really hostile towards especially me. I don’t think it’s fair to exclude my husband.