My nephew was arrested with heroin possession and has a court date in march. What will happen to him when he goes to court. We want to bring him to South Carolina for treatment. He is living on the streets at this point.

It all depends. Does he have a record, was he on probation or anything? I would suggest you do get him into treatment bubt maybe staying Texas. It will look better for him in court and lessen the chances of him getting arrested again or missing the courtdate. Make SURE he does not blow it off. That will just make things worse.
I have dealt with this a million times with my sons father and its stressful. You should try to get him help but of course if he doesn't want to get clean then he won't and you'll end up going crazy trying to help him. Where is he? Is he high etc.. I don't know your relationship but Id guess he has been doing this for awhile right? How old is he? Good luck!

If you can afford to be at court with him, do so. Or ask his lawyer to present your offer, with some background about you and your ability to pay, and maybe even some preliminary arrangements with a rehab near you without putting down a payment yet.