I have twin 4 year old daughters that haven't seen their father in 3.5 years. I want to file abandonment charges on him so I can sign custody over to my mother and step-father who are much more able to take care of my daughters.

You don't file abandonment charges, the children were not left without adult supervision.
See here: https://www.askmehelpdesk.com/family-law/child-abandonment-read-first-364259.html guardianship

If you want to transfer guardianship to your mother and stepfather, then do it. If the court requires that you get the father's permission, then you will have to do so.

Yes, what you ask is not what you need and not how it happens. You can try to get "guardianship" not custody, given to them. You will need an attorney