Can Grandparents Get Custody of a Child Left in Their Care

My question involves a child custody case from the State of: Colorado

My sister wants to move to Arizona with my niece and her boyfriend and leave my nephew with our parents. She has decided that she does not want to take care of him anymore. She does not have full custody of him and his biological father has been absent for most of his life. He also is an abusive stalker, I know that he was charged with assault on his ex girlfriends new boyfriend and I believe had a restraining order put on him.
My parents have been the most stable adult figures he has ever known, he is only five.

Do my parents have any chance of obtaining full custody of my nephew? What should my parents do to secure custody of him? If they are able to, would my parents be able to get child support? Please and thank you for any advice.

So if she doesn't have full custody of her son, who else has custody of him? BioDad?

The grandparents may be able to intervene in the custody case, depending on the full facts. The easier path for them, with the daughter wanting them to care for the child and the father absent (presumably for years) would normally be to pursue guardianship.

The tricky part here is that dad (who I am assuming to be the other party with custody rights) could decide he wants custody and, previously absent or no, that would make things much more complex for the grandparents.