How do you obtain a passport for your mother and father-in-law to travel from Mexico and stay for about two weeks?
They must get their passport in the country they are in. There is no way for you to get someone else’s passport. Sending them the money to get it would be the only way you can help. As far a visa is concerned (which you didn’t mention) It is helpful if you write a letter inviting them so they can take the letter to the US Embassy and apply for a tourist visa in Mexico.