Going for Sole legal custody

[lizzy]

I want to take my ex husband back to court to get sole legal custody of our 2 children. He hasn't seen or called them in 3 months, my son is always telling me things that go on there, he does drink and I am suspicious that he is doing drugs, because he did them while we were married and his father dealt them. I am going to be requesting a drug test. I know I do need some evidence of some things, but I also want my son to talk to someone in the court.  I want him to tell the judge or whoever what goes on and his feelings. He is 10. Now if I petition him to court and they can't serve him for the court date, what happens? He has no physical address, he doesn't have anywhere to live. What are my chances and what about not being able to serve him?