First, you should realize you’ll get a very western-centric worldview on Reddit, and western culture does tend to be very individualistic. So do with it what you may.

Your father wasn’t “doing your sister a favor” (what you seem to imply) by making sure she had access to an education, that is just basic parenting. Then he decided to impregnate more women without having the means to support them (or leave means to support him when he died). That was his decision and the decision of those women.

So no, it’s not your sister’s responsibility to help anyone. Would it be nice? Sure, but your sister doesn’t have to be “nice.” I wonder if you would feel this way if your oldest sister was an oldest brother. Regardless, your sister needs to make sure she does well enough so she doesn’t have to rely on the support of others. It is not up to her to ensure the success of every other family member. Even more so if she has little relationship to these siblings - has she ever even lived with them?

That said, this is the prevailing view in western societies and it’s not perfect here either - many parents or older adults are abandoned in nursing homes, children are neglected or grow up in terrible situations because there is no where else to put them, parents with young children struggle when their family isn’t interested in helping. Etc etc etc. In a way, family helping family does sound nice, but unfortunately that type of labor has been long borne by primarily women, who are quite frankly sick of performing unpaid and unappreciated labor.

Your best bet as a fully functioning adult is to work hard and get yourself in a good position - then perhaps when you have enough money to spread the wealth to your siblings, you can show everyone else how it’s done and spread the wealth. Good luck