If they wouldn't wanna see for just a vacation because you're choosing the healthier emotional situation for your family then you'd just have proof that you made the right choice.
I know how easy it is to pt yourself on that guilttrip of not being there for your family. My mom has cancer and I wanted to drop everything and move halfway across the world to be with her. Fact is though, that there are more things to consider, as your health and your finances. I made the choice of staying here til things settle down in my life, til the baby is born and I can be of more help to my family over there. Yes, you could say that you have enough money to support your sis. Is she going to be able to support herself though, when your hubby comes back and you need your money and time for yourself and your kids? Because if not, then there's no point in it all, right? If you are going to be on bedrest how are you going to be there for your Meme?
In the end you are going to have to think things thru a few times and follow your gut. You can be rational, write things down and keep that sticky on your fridge for emotional situations when you are going to doubt your decision. Or you could follow your instincts, it comes down to what kind of a person you are and how rational or not you have handled previous big matters...?
All I can say is that once you have made a decision either way you are going to feel better just for the fact that you can focus on the next step now instead of having sleepness nights over the same old issue, kwim? Win the next battle. Good luck to you!