THOMAS/MOUNTJOY/BRISCOE - previous threads (General)
The children on the 1871 census are William Briscoe's children from his previous marriage to Sophia Mountjoy who was sister of Mary Ann Mountjoy his second wife. 3 months after the death of Sophia, William married Mary Ann her widowed sister.
As for Mirah Thomas, she died in 1863 aged 6.