My gt gt grandmother Bridget Kavanagh was born about 1825 in Ireland, so it's doubtful she could be Andrew's sister as he was born much later, could be an aunt though, they seem to have moved to Widnes around the same time. Bridget Kavanagh married John Martin on 15/11/1841 at Wicklow, she died on 30/12/1878 at 9 Walmsley Street, the names of the witnesses on their children's baptisms included a Patrick, Michael, James and Mary Kavanagh, there were different spelling variations ,i.e. Cavanagh. I found who I think is your Andrew and Alice on the 1881 census, under the name Cavanagh at 63 Church Street. Margaret 13yrs born in Ireland, the other children all born in Widnes, Catherine 12yrs, Alice 10, James 7, Thomas 4, Annie,and Patrick 1 wk.
There were also other Cavanagh's in Widnes, a John living at 74 Oxford Street Widnes in 1871 and a Charles living at 8 Midwood Street, Widnes in 1891, thanks for your help with this, sometimes we can get a little clue

Pauline