my ex husbnad is going to hold an emergency custody hearing, what are the chances of him winning?

Hello, It depends on what he's alleging you did and what evidence he has.  If he's got evidence of you doing bad things, its possible.  However, the burden is very very high and most "emergency" motions are denied.  Ultimately it will come down to what he's got and what he can show. Without a lot more information, I cant really give an opinion about his chances of success.  If you're in the New Orleans or St. Tammany area, call The Civil Law Center, at 504-342-4221 and speak with an attorney asap.