There are companies that can expedite the process, but they are expensive.
In 2004 we returned to Guadalajara to visit family. My wife is a real cheap skate; she refused to pay for passports. Guess what, if you knew the movida you could get into Mexico without without a passport.
Unfortunately, getting back into the US is a different thing.
As soon as we got home, we gladly spent the money for the passports. Now you need the passports for sure. Also, you need to visit the Mexican Consulate and secure your permiso to enter the country.
If you are driving, apply for your auto permit at the same time. Also, be sure and purchase Mexican auto insurance. USA and Canadian insurance are not valid in Mexico.
If minor children will accompany you, make sure you have their papers in order. Problems seem to arise with step children and those whose relationship to you are not readily apparent.
Some people seem to come under more scrutiny than others. It is easier for Anglos than Latinos.
Good luck, and have fun.
Rufus