How do I go about getting custody of a 2 month old not blood related

She feeds him 8 oz bottles if not more at a time so she doesn't have to deal with him anytime I get him for visits with my son he is nasty stinks and always needs a bath and hasnt pooped in days dcs has been called she is always cleared I have videos of him screaming not happy and her poking and tapping his chest hard u can tell he is uncomfortable she is with a registered sex offender who she refers to as the babies daddy but is not she has took baby to the jail for visits. She says she will be with man in jail for sexual exploitation of a child weother she has to his it or not My sons father is actually the babies father she sends him to me and will oeave him for days at a time I would like legal advice of what I need to do to get the baby put of the horrible situation he is in.and she also has another child she lives with her sister and brother in law who are both on drugs what can I do