Will this work against my grand baby's biological dad?

the cyfd placed my daughter's child with us. she has a bad drug problem. we have helped her raise the baby who is 3 and when she got really bad, she left the baby with us nearly all the time anyway. well early on, the baby's bio dad's mother had him fighting for custody. well, he was given visitation. first supervised and then he was able to take the baby 2 times a week. he was also ordered to pay 400 bucks a month child support. we didn't like that he was able to take the baby, because the bio dad had some pot smoking issues. well, he stopped showing up and we never got any child support. this went on for, well almost 4 years. now that he's found out that my daughter is having these drug issues, he now wants custody. the baby hasn't seen him in almost 4 years. he told the cps that he stopped coming around, because we wouldn't allow him to see her. that's a lie. though we didn't like it, we had to let him, cause it was court ordered. can he get away with lying like this? we have a lawyer to fight him, but it makes me angry that he is such a liar. that's another problem we had with him as well. the fact that he's such a liar. the cyfd left her with us, but he plans on lying on us in court. we did have our battles with him and his family, but i sent him a fb message and apologized to him for the way i handled myself. he plans on using that letter against me. what do you think will happen with this situation? he chose to stay away for almost four years. no moral support, or financial support. 20 thousand dollars he owes. how can he just walk in and do this? i'm very worried about this. my grand baby has some issues over her mom's problems. i want to protect her. thank you..