If you are in charge of your daughters cell phone accounts you can block him from contacting them right now. Base it on his instability and facts. Do you really want an unstable addict having access to a 13 and 15 year old? The damage he could do to them emotionally right now is not worth taking that chance.
Protecting your kids at all costs right now is a must. Allow some counseling under their belts and yours then figure out a plan together for if or when he can contact them.