My Nephew Is Being Neglected, What can I do?

I have a 22 month old nephew and I take care of him whenever he is at my house. My brother is 19 and the baby's mother is 16. The babys mother is clearly unfit and neglectful toward's the baby. The baby constantly cries whenever we drop him off at home and would rather go to me than his own mother. The baby comes over all the time dirty with red marks on him and with clothing that doesn't fit him (0-3 months, newborn, 6-9 months clothing).The baby's grandmother is a drug addict and so is her boyfriend and they have already almost had the baby taken because they got caught driving with him and smoking crack in the car and the day the baby had to have an operation on his nose (He has a nose problem) the babys grandmother and her boyfriend showed up high at the hospital and stayed there like that falling asleep in the waiting room and everything. The baby only has one kidney and my mother and I were told that the baby should'nt have ANY form of medicine without having a doctor give the Okay because of his kidney, last week the baby had gotten a really bad cold and my mom asked his mother and other grandmother for his medicine that they give him and they gave her Children's dynatap and it clearly says on the bottle "Children under 6 years do not use". They falsely accused of child abuse once before claiming a scratch the baby had gotten from a toy was a "burn" and even the child service's lady said to us in her opinion it wasn't a burn. Anyway..when they falsely accused us of Child neglect his mom and other grandmother tried to say they were told we couldn't see the baby by Child services even tho they told us they can't say that and we ended up not seeing the baby for over a month because of them. Now, Today we were told the baby had to go back to his mother's house because he had a "Party" to go to and so we had to meet the baby's mother's drug addict step father at a store (We never give the baby to just him until today) and he was clearly high stumbeling and everything and he asked to use the babys stroller that I personally bought for him and I said No because I know for a fact they have a stroller that my brother's dad bought the baby and anyway so after The stepfather left my mom got a call from the babys drug addict grandmother claiming that if I didn't let them use the baby's stroller she was going to take us to court so we couldn't see the baby and she would drag it out for two years so my mom made me let them use the stroller..this isn't the first time they threatened us with not seeing the baby and dragging it out for two years..these people are crazy and the babys drug addict grandmother has 5 kids that she lost custody of because of how poorly they were taken care of and the babys mother shouldn't even be with her and when the grandmother was pregnant with her 6th child she lost it when she was 7 months pregnant because of doing crack and heroine while pregnant. What can we do to get the baby from these people?