OP, it's natural and normal to want a relationship with your parents and siblings, even if they are fucking bastards. You have the added problem of a vile (I don't doubt you) step-mother. Many people who are hurt as you are will return to the source trying to find the love that is missing.
You need therapy. I speak as someone who has had plenty! So much that it changed my life. I did it all NHS, so lots of pushing, lots of waiting, lots of preparing myself for each set of six sessions.
You are only 28. You can have a much happier life if you address this matter in therapy. You've been very, very badly treated by both of your parents and your stepmother. You know it. You don't have to cover it up, even to yourself.
Am I right in thinking you're rebuilding your relationship with your mother? It might be possible to do that with your father too - but perhaps it would be a good idea to allow that, after you've tried, he might be a dead loss, worth nothing more than minimal contact. The stepmother, well, I wouldn't waste another moment thinking about her. Who deliberately hurts a child? Not anyone who deserves consideration. You're not bound to her by dna, so just let her go.
My situation now, as an older person, is that I'm caring for my dad. The one who didn't love me (still doesn't), didn't believe I was his child (until we were dna tested), has no respect for women anyway. He and my brother still mock me, take the piss, take advantage and laugh at me while they're doing it. I do what I do because I'm a good person, not because I hope for any respect or affection from them. After therapy, I can make a choice. If I chose, I could walk away without causing myself any particular pain.
It will sound like tosh but mindfulness works. Eventually. I'd taught it before it genuinely worked for me. A self-compassion journal helped. I went back to the toddler I remember being, and talked to her in my journal. You could go back to your child-self and talk to her. Again, sounds like codswallop but it helped me heal a little, and recently it's helped my dd, too.
I feel for you and wish you well. Good luck.