Families seldom match the story-book ideal. Parents often are far from perfect, loving, understanding, forgiving, selfless people; more often, they are dealing with the dysfunctions they were raised to think of as normal. Guilt, resentments, revenge, tit-for-tat behaviors, withholding love, bribing or buying love – it's the stuff of operas, movies, and everyday life.
You might be in a much better emotional state if you just learn to see what is true rather than wishing for your parents to be what you think they should be. If they are not loving toward you or able to receive your help, then you might need to reassess what you can reasonably do for them. There are people who are able to give unstintingly to people who do not give back, and there are people who will quickly become burned out by what they feel they must give.
You can't be responsible for the choices your family makes. You really have little-to-no control over their attitudes. It sounds like you are all stuck in old patterns that just do not work. As long as you try to make your family be (in your own mind) what they are not, you will struggle and feel a great deal of grief. But if you can back away and take a longer view, you may be able to make saner decisions about what action you will or won't make.
If you can do this, perhaps you can even influence your siblings toward making decisions that can actually effect some real changes that will work better for all – perhaps even better for your parents. But do it for yourself, for common sense and sanity, not because you expect others to understand or appreciate your choices or reciprocate. They may not.
There's a self-help process called The Work that can help you get to a clearer place, if you're interested in trying it. Check out http://thework.com/thework.php. Wishing you well!
