Blood is not the end of the world; we don't love people because they share similar dna, we love them because they're people. If you don't have a family you'll soon discover that the friends you associate with, and the people you love to be around become your REAL family, blood doesn't mean anything.
In life they'll be plenty of chances to mentor younger generations, and you'll soon find that it's these sort of relationships that will grant you purpose in life ebcause they take on the parent/child dynamic, which is fulfilling.
I think all adults have the responsibility of treating younger generations as their own children, because it's through this that a lot of purpose and happiness is formed, it shouldn't die or end at blood, it may very well be possible that you'll never have related family, but like I say, blood doesn't mean anything, in the end it's the people that mattered, not the blood.