John C Costin seem to be half White, half Mexican, a so called mulatto. He is also enlisted as White. He was a Latter Days Saint (Mormon). He married Dora Johnson, a black woman. They married very young (than by law allowed). They had their kids (in the good Mormon tradition) shortjy after marriage. In the census it seems the year of birth to be far off the real date, just to avoid any problems with authorities.
Their (first kid) daughter Dora E married very young with Samuel A Lawson. In the census information one sees that her age cannot be right according to normal marriages (at that time), the later census information might be more to the truth. She must have been of light skin as she was enlisted as White.
Dora and Samuel were not buried in the Mormon graveyard in Ouachita, Louisiana, as some of her siblings and parents were. They must not have been involved in the Latter Day Saints believe too much. She might even have used Samuel to get out of the tight rules she had at home or it was pure love between two youngsters that broke all normal rules of life at that time.
I am still looking for more confirmation for above story, Dora and Samuel death certificates do not mention their parents at all. Dora's parents were still alive when she died. Thomas might be more complicated as he probably was raised by his Step Mother (Sarah A), his parents died when he was still young. He might not have known the exact information about his real parents.