For what it's worth, I'm in my early 40's, female, and graduated from college with honors. It's possible to go through school, and it's possible to pass exams even with severe symptoms of memory loss and other symptoms of complex post-traumatic stress-disorder.
But the symptoms can be debilitating. I lost my favorite job when a coworker stole from me. I dissociated and went into a fawn response, working for 48 hours straight compulsively. This was a coping mechanism my parents created in me. As a child, I knew that when they started destroying or stealing my property, they were about to do something emotionally devastating to me if I didn't overwork and please them somehow. When triggered by the event at work, my brain slipped into that behavior. But I worked in a secure government location. By staying overnight and working for two days straight, I unintentionally compromised security and made myself seem like a risk to client records. I was rightfully fired.
I didn't remember much about those 48 hours. I don't remember what I did when I fawned for my parents as a child. This is where some of the lapses in memory happened. Sometimes it was because I was being abused and I just dissociated to escape. Other times, I was reminded of past abuse and my brain didn't know it wasn't a current abuse situation; my brain dissociated to escape and protect me again. Our brains forget to protect us.
Because I have CPTSD, I can't be around startling aggressive animals, like dogs or humans, for that matter. So I can't work my dream job because there would be aggressive abusive people as an expected aspect of the work. (I wanted to be an attorney for child abuse victims. I now know that's not something I could do competently in my current state of mental health.)
I can't be around certain smells or places that remind me of my parents. I can't enjoy specific sex acts. I can't watch certain movies. I can't eat certain foods. All these things can cause intense symptoms of dissociation and memory loss for me. This is common of many people who suffered consistent abuse or emotional incest by caregivers that didn't seem escapable.
But what I, and other people with CPTSD can do is to minimize our suffering and dissociation by avoiding those triggers. There are trauma-treatment specialists who can help us soften those triggers and the resulting symptoms so our lives are not so limited.
Do not be hard on yourself when you realize you have to avoid stimuli to reduce flashbacks. This is part of what it means to take responsibility and bear the loss of the abuse we suffered.
But, again, you have to get out before you can even start to soften triggers and work to regain your ability to remember. Don't worry about the memories you've lost. Don't try to remember, yet, if ever. Your mind blocked them out to protect you. Psychologists now don't think it's even necessary to remember in order to regain memory skills as an adult or heal from the trauma.
Just take what comfort you can from the fact that learning and memory skills are possible to recover. You can likely go through college and get a good career, but you'll have to work with effects of the abuse your suffered like a person who suffered irreparable amputations and head injuries from a car crash. You can't regrow limbs, but you can learn how to walk with prosthetics and hard work.
But you have to get out of the figurative car. You cannot heal when the abuse is still happening and you still feel trapped.
You've got to get distance from the situation before your can have any perspective on just how bad the figurative car wreck was.
If we just look at your situation as a car wreck, metaphorically, then your parents are driving, you're a passenger, and you're trapped in the wreckage. You can't assess your injuries, but you know you're injured, can't remember the accident, and all you see is blood. You don't have the training to repair your injuries, but your parents are still fighting, maybe setting the car on fire to hide the fact they caused the accident.
You have got to get out of the car. Maybe the injuries were slight and cause no scars. Maybe you've lost all limbs and suffered brain damage. You can't get rehab or therapy until you know. At the very least, you've got to survive and heal well enough to research how to heal the scars yourself.
Don't worry about your mother. You cannot get her out. She must get professional help for herself or get the nerve to do it on her own. You can't worry about your stepfather.
Just worry about yourself. Get out. Get help if you can. Get as healthy as possible. Get safe and secure. THEN and only then should you even consider trying to engage your abusers in any way other than superficially.
(I'm not a therapist. I'm speaking from personal experience as a survivor of emotional incest and someone dealing with complex PTSD. My perspective may seem mild or extreme. I'm viewing your situation from my own very skewed lens of experience.)