Can an adult offender get full custody of his children?

My ex-husband and i are in a custody battle. I have previous drug charges, and he is a registered offender (over adult charges). dhs has an open case on me for failing a drug test for marijuana. some how another he ped his test. i have ped every test since, only failed the once, even went to rehab. he lives with his mother and sister in their 3 bedroom home. i live in my 3 bedroom home with plenty of room for the kids, can he get full custody of our children and step parent rights to my other child?