My father-in-law believes he has a claim to US Citizenship through his deceased mother.
He was born in Mexico on 3/8/1939 .
His mother was born in Texas on 10/8/22 in Rio Grande City, Texas .
She married a Mexican National. They lived in Mexico and US throughout their lives together.
Her son, my father-in-law, was born in Mexico on 3/8/39 and currently resides in Mexico. All of his children including my wife were all born in Mexico.
His mother died in a hospital in Corpus Christi, TX on 10/12/95.
We have her death certificate and social security number. We are in the process of obtaining her birth certificate also.
My father-in-law currently has a US Visitor's Visa.
After the death of his wife in Corpus, his father moved back to Mexico and just recently passed away a couple of years ago at the age of 100.
Is it true that my father-in-law could obtain a US Passport by going to a US Passport Agency and submitting evidence to the above?
What exactly would he need to provide?