I would say my obligation to help is relatively minimal, because for most of my adolescence and all of my adulthood, I have been left largely to fend for myself while my parents focused on what they viewed as the more immediate needs of my siblings. Starting from when I was about 7 years old and my eldest brother developed a drinking problem and had major behavioral issues. I have always been "the good kid" -- good grades, no behavioral issues, went to the inexpensive in-state school because it was easier financially for the family (despite being accepted to several much more competitive colleges), self-funded grad school, totally financially independent, paid for own wedding and home (none of our siblings did this), and have received zero help from parents for kids (not financial, no childcare, not even emotional support really as we both had siblings going through major upheavals when our kids were born and family focus was on that).
So I feel that I have made my contribution. I've been in therapy (that I found and paid for -- my parents have paid for therapy and even in-treatment mental health care for my siblings, my ILs have done the same for my BIL) since I was in my 20s to deal with issues from parental neglect, major people pleaser tendencies, and just kind of learning from scratch that it is okay for me to have needs and to ask loved ones to help meet them. I had kids late in life specifically because I felt I needed to address those issues before I had them (all my siblings had their kids young, not one of them thought "maybe I should deal with my mental health or addiction issues before making myself responsible for someone else's well being). I also got married later for the same reason (two of my siblings are divorced and my parents have helped them financially and with things like therapy and moral support through those events).
So I have a mentally healthy and financially stable life because I figured out how to make that happen, with very little help from my family. Certainly zero help from siblings, though I am grateful to my parents for paying for college at least. That was my contribution -- to have no needs within my family. But no, I am not going to take money away from my kid's future, or from my retirement, to throw down the bottomless pit of assistance that my siblings, and my BIL, have established with our parents. They will need to figure it out. I wish them the very best of luck (not sarcasm, I really do).