File for full custody

What are the steps I need to take? How much does it cost to file? Does anyone have advice for me or has been through this before. My children’s dad lived in pa ( I live in Ohio) and recently moved to Nd and doesn’t talk or check up on his kids. He’s also under child support too. Which I found out yesterday they didn’t even know he moved states. I’m looking to get full custody of my two girls. He wanted to pay for the filing fee for my significant other to adopt them. Even though he owed 1200 in child support. My point is he’s a pile of crap. So any advice would be great. And btw I don’t know his new address and he won’t give it to me. So idk if that’ll be another issue