I'm not going to say he will or wont get it but a few things need to be taken into consideration here.
Depending on what state they live in will be a determining factor. In most cases, yes the Mother will get at least residential joint custody but it also falls under guidelines of income as to who has the best ability to financially take care of the children sometimes. If the state they live in is a mothers rights state, they would basically have to prove she is either a severe druggie, beats the kids and neglects them, or that her job is to demanding of her to be able to watch over the children and care for them adequetly.
Obviously there are other things that will be looked at but those are some major determining factors that i listed...