Legal Question in Family Law in California

Well, you can click this link: http://travel.state.gov/content/travel/english/legal-considerations/judicial/country/paraguay.html Then click the tag for "service of process," follow those links and best of luck to you.

Or you can hire a lawyer who has done international service of process under the Inter-American treaties, although attorneys with The Hague Convention experience can probably figure out the Inter-American versions. I personally have only worked on cases that involved Hague Convention signatory jurisdictions.

P.S. If they have already appeared in the action you probably are legally allowed to serve them by mail, but of course enforcement of any judgment or order would still involve using the international legal treaty processes.