The Rowland Hughes with parents on 1841 census aged 20 cannot be the same person if he was married in 1836.
On 1851 census there is a Rowland Hughes b. Trefdraeth with wife Mary Rowlands born Llangefni 1815. with children Hugh b. 1837, Jane b.1839, John b 1841,Anne b 1844 all above children born at Trefdraeth ( in the district of Llangristiolus ) and son Daniel b 1845 born at Holyhead.
Rowland Hughes is a Sailor and they are living at 17 Moll Bank, Holyhead.
There are 2 Rowland Hughes born at Llangristiolus district to a Richard 7 Margaret Hughes one was born 31 March 1821 chris.6 Apr.1821 & the other to same parents on 18 Dec 1818 chris. 6 Jan 1819. That information is from Family Search.