Military Hitch

My husband (we were married May 25th) was deployed to Korea for a hardship tour this past monday for 18months. When he gets back, he wants to try to get full custody of his two year old son with his ex. She has thrown knives at him, filed unjustified restraining orders against him so that he cannot see his son, has even taken his son to homeless shelters so that my husband couldn't find him. He wasn't even able to see his son before he was deployed. But there is another hitch...when we had a bad falling out last september and split up for a month, he ended up sleeping with her...and yes she got pregnant. There is a possibility the baby isn't his because she had a steady boyfriend at the time. She told him she would put it up for adoption, but has since decided to keep it in hopes that he will come back to her, but she doesn't know we're going to try for custody. My husband doesn't want custody of the 2nd child. Will it be possible to get custody of the first and not the 2nd?