My Great Grandfather was John Miller of Philadelphia.I know very little about him.
I could not find the census records you referred to in 1850, Thomas and Martha Marshall living with Richard Marshall.I did find Thomas Marshall, age 72, living with Richard Marshall in 1860.The only Martha in this household was Martha Marshall, age 28, perhaps a sister of Richard.
In 1850 I did find this census record in Newton Township, Camden County.
Thomas Marshall, age 62 Martha Marshall, age 60 Elizabeth Marshall, age 29 Martha Marshall, age 21 Thomas Marshall, age 21 Esther Marshall, age 83 Thomas A. Matlack, age 4 Martha Ann Matlack, age 1
62 and 60 are the right ages to be your Thomas and Martha.
Joseph Ellis Matlack, born 7 November 1820, died 12 June 1849, married 25 December 1844 Elizabeth Marshall born 9 December 1820, died 8 January 1872.
Joseph and Elizabeth had two children, Thomas Albert born 18 March 1846 and Martha Ann born 1 February 1849.I think Elizabeth Marshall, age 29 in the census record is the mother of Thomas and Martha Ann Matlack.Esther is probably the mother of Thomas Marshall, age 62.
Joseph Ellis Matlack is my first cousin 4 times removed and I have his ancestry.I have not been able to Identify Martha Matlack, born 1790.