Just getting back to the topic of this thread, in case anyone searches for a good notary in the future, we used Notary 20 - Benjamin de la Peña Mora. This was to setup 2 "corporations" and some immigration paperwork. - NOTARIA 20 Lic. Benjamin De la Peña Mora - Very pleased with their service, though not the cheapest in Cancun.
The recommendation of the Notary certainly does fit the title of the thread, and will be useful. Although Mexico does allow- those who are given resident visas- permission to sponsor family members, and even SOs, some people would pause when they consider that, in regard to an SO, filing the documents to support it is a step from which there is no going back, and could carry unintended consequences, as it is a judicial admission of the existence of a relationship that many countries and states would recognize, and attach legal significance to.