Stuck in middle of a web of responsibilities and evil stepmother

I (25) am the eldest son in my family, therefore the responsible one in the house. I have a younger sibling as well. My mother had expired when was 11, and my father later remarried so that me and my sibling would be nourished. Good thought, bad decision. Stepmother is very bad, doesn't care about my maternal relations or paternal relations at all, but forcing her relations, where her family is worst piece of shit. They have badmouthed my family dozens of times in front of me and my sibling, but we didn't say as we were kids and wanted to avoid any sour relations. Always conspiring to break us apart from all of our relatives and she is succeeding.

I am not telling my father or calling for divorce, because I believe he'll need a partner in old age, but at the same time, relations are also needed, as part of the society. As an introvert, I don't have any friends either, and relatives are gradually going away, or I should say, went away entirely. She illtreats our guest, doesn't behave well, and guest just leave for their own peace and don't talk back to us until or unless there's a societal formality. She doesn't talk to any guest, completes ignores them and doesn't offer them food

I started from a humble financial background, and I invested my entire life to make a decent living, thinking that money can solve all my problems. It did to some extent, but now her behavior is making it very hard. She and her relatives are sweet mouthed to me now, since I am earning, but I can see the facade. They still don't treat my sibling well who's still studying.

I think getting married myself may shift the societal responsibilities entirely to me, but I am also perplexed whether the other person will be treated well by her or not. I am stuck in this and while trying to solve my problems I don't want to make it harder for someone else and have been evading any suits. Additionally, I still don't have any savings for a good gathering for marriage and not to mention the bride's side of family as well, not too show-off but atleast all the people who have supported me so far. I don't have a good house either although I can rent a property someplace else if needed, as I work remotely.