I am glad for you that you have a friend willing to help you any way they can. I am sorry your sister has passed judgment on you without collecting all of the fact. I am sure that hurts deep right now.
YOU know the truth, YOU know what is best for you and the kids and your sister really has no clue. Dont let her judgment on you stop you from doing what you can to save you and your kids.
Once he is gone and he starts the guilt trips or the begging to come back, try to stay strong and refuse. He will play all the nice songs of change and doing better and all the things he knows you want to hear, but try to remind yourself those are only words. His actions were neglect and abandonment. Try to hang on to that to be able to move forward.
If you can, see if you can get the courts to order support. Most courts now take the support directly out of the check so the person supposed to pay cannot "forget" or claim they dont have the money.
You might see if someone around will barter something with you, they fix your car and you____(insert here what you are good at and can physically do that the person fixing your car would want. This could be cleaning a house, making gifts for the holiday, watching the kids, doing the laundry/ironing, etc. stretch your imagination)___.
what are the ages of your kids. Depending on their ages you can either have them help you with tasks around the house and yard while you try to earn extra money, or if they are young enough, check with the state laws regarding in home day care.
Have you spoken to your land lord regarding your situation? Maybe knowing the situation he/she might be able to work with you on rent, if they are not willing, best to know now while you have time to relocate to a place they are willing to work with you.
do you have a city transit system where you live? where as staning out waiting for the bus and trying to make the right connections is a hastle, and in bad weather miserable, it is an option if it is available. Also you might see if someone around might know of employment opportunities and maybe willing to carpool with you until your car is fixed...
It is not completely hopeless, the biggest challenge you have is your physical handicap, and I am sure you have learned ways around those barriers already or are learning ways around them.
Hang in there, again I am sorry your sister doesn't get it, I doubt she will unless she finds herself in that kind of spot. Maybe next time she starts judging you and condemning you ask her how may year has she lived in your shoes and lived with him to know exactly what she is judging you on.
Stay safe and be as strong as you can, especially when people start yanking on the emotion strings.
Kat