I am a grandmother who have a 16 yr old daughter with a 9 month old son. She stated to me that she can not do this no more (meaning she can no longer take care of the baby).I take care of both of them finially and emotionally. I was wondering how do I start the process of getting legal custody or parental custody of my grandchild

Try first for legal guardianship. This will be easier to obtain and give you the right to make decisions for the child.

I would suggest retaining an attorney.