Awww Maura that really sucks and I know aside from all the anger, it's probably pretty painful too.
Here's what I would do- I would let your sister do what she wants. If she doesn't show up to anything (including the wedding) that's on her. She will feel like shit later if she's a good sister. I know you want her to be supportive and to be a sister, but apparently she's a little self involved at the moment.
Last minute, she doesn't come- why not just have another friend act as MOH and hold your flowers, help you primp and do all the other MOH duties. It's not worth all the stress. As for your whole family drama- again, that's on them. If they can't afford to go then what are you suppose to do? Most of Jose's family is in Mexico right? How does your family think that probably should be fairly solved? If it's cheaper for you guys in the long run and less expensive, do what you need to do and forget about all the people who aren't helpful along the way.
In the meantime, I'm really sorry you have to deal with it all. It's worth it in the end.