Mother is getting weaker by the day and so am I

It is so hard with me all the way in Las Vegas while she is in Hawaii. However, I can't go and stay in Hawaii. I have a husband and daughter that need me as well as dealing with my own medical issues. I am trying to get my sister to go to Hawaii to at least try and help a little, but she is so selfish I don't think she will. She has not seen my mother since this started. She even refuses to talk to her on the phone or even email. I don't know how to help them. My older sister who is currently taking care of mom, has two very active children and is finding it hard to make time to take care of mom too. Mom hasn't even began chemo yet, which should make it even more difficult for her. I am worried about what will happen once it starts. My mother would get much better care here in Vegas, but she refuses to leave Hawaii. Right now we are just allowing her to do what she wants.She deserves it. Since I do not work I would be with her everyday to help even just to make sure she is eating. Grrr I am so frustrated and scared. I will probably end up having to go for who knows how long. I have major anxiety all the time. Even to the point that I am getting major chest pains, but I don't want attention to be drawn to me instead of the person who really needs it... MOM! The summer has always been the time I spend real quality time with husband. He works for the school district and therefore has summers off. My daughter (actually step) goes to San Diego for the summer to visit her mother. So usually it is our time to rekindle our relationship. We take camping trips, go fishing, he umpires and coaches baseball so I go to all the games and provide oranges and refreshments, I basically enjoy my life during the summer. It's like hubby and I have a summer honeymoon time every year. How can I leave him for 2-3 months. I feel guilty. I want to help my mother terribly, but I also need this time with my husband. During the school year he works 12-14 hours 5-6 days a week, so I barely see him. I am so lost, feeling guilty, angry at my twin sister who refuses to help, disappointed in myself that my older sister has to take complete care of our mother, upset my younger sister is too self involved and young moving to LA to be "found" as an actress. All the stress falls on my older sister and me while my twin and younger sister just skate by. I have migraines daily, so much that I am in the ER every week. My chest pains started 3 days ago and while they make me nervous, I can't take the time to deal with it. Help me someone with some advice to get through this. I am scared to end up in the hospital myself and then really not be able to help out. I want to stop crying everyday,and not sleeping because I can't get my brain to relax.