@Justmerach , I agree with @byfaithandnotbysight - this sounds like more than just a forgiveness issue on your mum's part.
Forgive me for being blunt, and I say this out of a sense of concern, but you sound very vulnerable. I have read many of your posts and you appear to me to be almost child like in your trust and naivety- you have shared a lot on this public forum that has disclosed who you are. I am sending you a hug (((Justmerach)))
You are doing ok! Autism is a disability covered by the Equalities Act 2010. However, that label does not define who you are in Christ. If you allow Him, and it sounds like you do, He will use your superpower.
You are doing ok! You love your dad, and do your best for him.
You are doing ok! You love your wider family and do your best for them.
You are doing okay! You love your mum and do your best for her.
You, @Justmerach are doing ok! You are not responsible for childhood hurts done to you. You are not responsible for how your parents act now, nor historically. You are not responsible for how your mum feels about your dad, nor for the dynamics of their relationship.
Share scriptures and the Gospel by all means, but the bottom line is, your mum, dad, and wider family - they are all individual human beings, and their relationship with the Lord is uniquely their own. With the proviso you do not cause them to stumble, which, it is clear you do not, you are not responsible for their walk.
The LORD is my strength and my shield; my heart trusts in Him, and He helps me. My heart leaps for joy, and with my song I praise Him.