I'm kinda in a similar zone. My father didn't take any responsibility for his father (my grandfather) and left him to die, didn't bother about wife's health(mental/physical) who's traumatized by this marriage arranged by elders and only living considering the future of her two children. He failed to provide for children the support of a father - which I can understand if there's any genuine reason - but him being a psychopath - was only my mistake to expect
Despite several aspirations I had to take up responsibilities early - Father got admitted in ICU twice eroding all savings personally of mine, asking for relatives and friends for support, arranging for grandfather's funeral, and marriage for my elder brother etc.
In this case - with my limited experience, I'd say
Try to enhance skills and grow rapidly - job switch etc. till 26,27,28 years of age
By then brother should likely finish graduation - talk to brother about the responsibilities and life so that he is realistic and plans the future about getting a good paying job etc.
Staying with family till brother finishes his education is what I'd do. But at the same time I'd be enhancing my career as well.
Marriage is not a solution right now and it would add more to one's responsibilities. Let things settle. This too shall pass.