Mulvey family emigrated to Sheffield 1850s?

My great-great grandparents were both born in Ireland; Martin Mulvey about 1832, possibly from Roscommon , and Julia Hogan about 1836, from Tipperary. They were married in Sheffield, Yorkshire in 1857. Martin’s father is given as Andrew Mulvey, farmer, and Julia’s father as Patrick Hogan, deceased.

According to the Sheffield Indexers there was a Patrick Mulvey buried in the same plot as members of Martin and Julia’s family. In the 1861 census (surname spelled as Mulvay) he was living with his wife and children and also two brothers, Andrew and John. So, these could all be brothers of Martin. Patrick was born c.1828, Andrew c.1834 and John c.1836, all in Ireland.

In the 1871 census, the household of Martin and Julia included Kieran Mulvey, born 1850 in Ireland, who was described as a brother to the head of the family. Also Timothy Hogan, born 1840, who was Julia’s brother.

In the 1911 census, it states that Kieran Mulvey’s place of birth was Roscommon, and the townland or parish has been transcribed as Clamoster although on the actual census page it doesn't look like that.

Griffith’s valuation shows an Andrew Mulvey in Camlagh, Taghmaconnell, Ballinasloe with George Newcomen as landlord. Ballinasloe is stated as being in Roscommon but now seems to be part of County Galway.

Tithe Applotment books 1828 show Andrew Mulvie senior, Andrew Mulvie junior and Patt Mulvie in Culliaghmore, Moore, Roscommon. From 1828 – 1842 there are also several other Mulvey entrants in Roscommon.

Family Search has a death record for Andrew Mulvee in Ballinasloe in 1882. He was born c. 1807 which puts him at about the right age to be the father of Martin and the others.

I can find no birth records for Martin Mulvey or Julia Hogan on RootsIreland.ie.

Any help as to where these Mulveys were from would be greatly appreciated.