First of all, let me say that I am not related to this Allen family, but I can tell you a few things that I can see on-line.
I believe that the man you are calling Tom S., is actually Thomas L, or at least that is the way I kept seeing it.He was born Feb 1876 in Mississippi.He has a sister named Ethel, born Jun 1880 in MS.I can see them in Montague TX as early as 1900.His parents names are Russel J, born Alabama in Mar of 1849, and Arminda born Alabama in May 1852.On the 1900 census it shows Russel's occupation as a blacksmith.His mother shows she is the mother of 4 living children and they have been married 31 years.
Just under this family is a Jasper Allen born MS with parents both born Alabama which appears to be another son of Russel above, and he is also a blacksmith.He was born May 1870 and has been married 10 years.His wife is Callie born Nov 1872 in Mississippi.Children are Flora Sep 1891 TX, Dana Mar 1895 TX, and Dovie Oct 1898 TX.His wife states 5 children with 3 living.
Going back to 1930 I can see Thomas L Allen born 1878 Mississippi and wife Ada born about 1889 Arkansas.Children are Arminda 10, Russell J 9, and Floyd C 6.Also shown are Russel J, age 70 and Arminda 69.
It looks like they came to Texas in the ten years between 1880 and 1890 by looking at the birth of the children.
I can see them in District 5, Alcorn County, Mississippi in 1880.The family looks like this at that time.
Russel J. Allen, farmer, age 31, born ALboth parents born Georgia Armindia Allen, keeps house, 30 AL AL AL Jasper M Allen, age 10, AL AL AL Dephodill (female, age 6 MS AL AL Thomas L, age 3 MS AL AL
So that gives you the names of all four of Russel's children and establishes they left Alabama for Mississippi between 1870 and 1874 based on children's age.