Thanks for all of the responses. Unfortunately, I don't have the time/energy to quote and paste all of the questions that deserve answers, so I'll do the best I can to answer some of them here:
~ Concerning Brother #1: Although his wife is disabled and receives SSI, she is able to take care of herself. Brother does not have to take care of her in any way. Concerning his ability to pay for mom's care.......he has bragged to me in many emails that he is financially secure and that caring for mom is no big deal to him financially. As far as the fact that they do not take vacations or purchase luxury items, they are extremely frugal. She hates travel, has some phobias/anxieties that prevent her from flying (and even from driving over bridges). They are very simple people. They are happy with simple things. They married later in life and chose not to have children. And yes, he is the brother who will be taking Mom in at some point (at least that's the plan) due to his proximity to good hospitals/doctors, as well as the fact that his wife is home all day and can keep Mom company (they have an inlaw apartment, so it wouldn't be constant togetherness). I have no problem at all with him getting all of the money from the house (and that's all there is as far as "inheritance" goes). Caring for the elderly can be very expensive.
~ Concerning my getting a part-time job: I teach young children, and do not have the expertise to tutor in areas where tutoring is in high demand. I have made the decision not to work part time, because my ex doesn't have the girls as much as many divorced dads have their kids, so my girls would be alone while I'm gone. We've been through a very traumatic divorce (he abandoned us for a girl who is young enough to be my daughter, and has basically chosen her and her children over us), an upsetting move, and I feel that they need me to be HOME. We all know how important it is in those tween/teen years to be there for your kids and to know what's going on with them.
~ Concerning my other "choices", I am pretty surprised at the rude speculation done about my lifestyle, while at the same time people speculate that my brother is some sort of saint.

While I was married, we went on two vacations: one to Washington, DC (driving distance, 2 night stay, all free museums), and one "once in a lifetime" trip to Disney World. Since then, my DDs and I have done nothing but a few day trips and visits to relatives/friends. I have never had a new car in my life. We all pack our lunches every day, and have never had manicures/pedicures/salon haircuts. My daughters have given up horseback riding and dancing lessons, and even school trips (not field trips, but overnight trips) due to lack of finances.
Brother #2 has told me not to worry so much about all of this, but it has made me feel terribly guilty (and I must say that many of your posts made me feel even worse -- I don't mind the advice, but the "shame on you" attitudes were a little too much).