Locating and serving

As a victim of domestic violence, I have a no contact order in place and am not currently aware of where my husband is living in order to serve him papers. I have an address that I believe belongs to his family but no way to verify it. I have done an online search/background check via a paid site with no usable results. I have looked into hiring a private investigator but their cost is outside my budget as a single mom getting no child support ($300-$600+). The cost of the paperwork is already stretching my budget.
My question is, if I send the paperwork certified mail to the address I have and someone in his family signs for it, will it be considered served in court? Or, if I have the sheriff serve it and he is not living at the address I have, will they attempt to find a newer address and serve it there? Thank you.

If he has already been served in the underlying action, you can serve subsequent papers at his last known address (or the address at which he was served/the address on file at the courthouse). If you serve the initial action and ex parte order via certified mail and a party other than him signs for it and you have no proof that he lives there, it will not be considered good service.