I found on Familysearch.org a baptism for a Sarah Hughs to Thomas Hughs & Susanah Williams born 26-2-1826, baptised 29-4-1827 at Independent, Rhosllanerchrugog, Dengighshire. (Hughes spelt here without the e.)
This could be a sister to Mary & Thomas. Does The Blackwell Index cover this area?

I looked up Rhos & found " a village originally within the ancient parish of Raubon and the district was referred to as Morton Above. In 1844 Morton Above became part of the newly created parish of Rhosllanerchrugog.
This ties in with the family on the 1851 census living in Rhos, Morton Above.
Your thought of 2 marriages is also entirely possible.
Karen