Which is better for my situtation temporay custody or guardinship?

My duaghter will be 19 yrs old next week. She has a baby that is 3 months old. The babies father, her boyfriend she lives with him and his dad. She decided that the baby would live with me and she could visit. I made the offer she accepted. She moved in with me 2 days ago. I really want to raise her because that is best as long as drugs are in the picture. I don't want problems with my daughter either. Do I need both signatures from mom and dad? They are not married but baby does have his last name. I Guess I want to know that I have control of the babies best interest that they just come and say I the mom or dad I am taking her when ever they fill like it. Which is best? Do you have to go to court with either? I think she is willing to sign.