We have some friends who after working in Mexico for about 5 years, retired and bought a home there. It is outside of Cuernavaca in a little town called Teposlan (sp?). they swear it is safe but have given up on us visiting them. We won't go there. After 40 years of hunting on both sides of the Rio Grande we had several scary things happen to us and that was before things got really bad down there. No more Mexico for these native Texans!
We have some friends who after working in Mexico for about 5 years, retired and bought a home there. Too bad your friends didn't closely study the Mexican laws regarding resident aliens before deciding to buy property there. They're pretty harsh, by American standards. Can't vote, can't own firearms, don't have the same property rights as Mexican citizens, etc. Legal immigrants are definitely second class citizens there.
And with the increase in serious violence there, I honestly don't see what the draw is. Hopefully your friends aren't stuck there.