There are some very good researchers that browse this forum and have access to sources I don't have. They might be able to help you, but you didn't include any dates for anyone in your query, it helps to narrow down searches. Without dates I can't be positive I found some of the brothers, but these three all born MS and birth dates fairly close to each other.
Upshur Co, TX -- Samuel McNair b 1847 MS and his family Navarro Co, TX -- Alexander McNair b 1836 MS and his family Hunt Co, TX -- Henry McNair, b 1839 MS and his family
By following members of the family you might find living members.
TX Dth Idx thru 1976:
Name: A.A. Mcnair Death Date: 17 Aug 1943 Death Place: Fort Worth, Tarrant, Texas Gender: Male Race: white Death Age: 55 years 4 months Estimated Birth Date: 1888 Birth Date: Birthplace: Upshard County, Texas[should be Upshur Co]
Marital Status: Married Spouse's Name: Father's Name: Hugh A. Mcnair Father's Birthplace: Mississippi Mother's Name: Martha S. Payne Mother's Birthplace: Alabama Occupation: Guard-Burns Dective Agenc Place of Residence: Fort Worth, Tarrant, Texas Cemetery: Winsboro Cemetery Burial Place: Winsboro, Texas Burial Date: 19 Aug 1943 Additional Relatives: X Film Number: 2137435 Digital Film Number: 4029600 Image Number: 155 Reference Number: 39549
Informant was his wife. His obituary might list survivors, good way to find married names of female members of the family.