Richard and Sarah both go by Robinson, never Emmett. Also, Sarahs marriage cert she has no father listed. Why would she not add Thomas, especially seen as he died very young and she was the informant of his death. I would imagine any daughter whose father died so young would want to carry his name.
It is possible, but even if they had them out of wedlock, why would they not change to Emmett?
No, I genuinely believe they were Hannahs, especially considering she was 5 years Thomas' senior.
I now need to trace his lineage. The oil painting I have as a profile photo looks very much like my late Grandfather. This man is named as William Emmott 1809 - 1879. Potentially a brother of Thomas maybe.