Family History search: Robert Rigby and Mary Regan

Robert was born 1887 father William, mother Jane.
Mary was born 4th June 1889, father Hugh, mother Emily (Murphy)
Mary married Robert 14th August 1910 at St Judes (and again at St Mary of the Angels 19th Dec 1911). Baby Robert born 1st October 1911, died 25th and buried 28th in Walton Parochial Cemetery.
Problem is that I can't so far trace Robert after 1911.

My Dad was born April 1918 but no fathers name shown and Mary registered him as Charles Regan. Mary subsequently had further children, Hugh born and died 4th Qtr 1924; Mary in 1926 and Hugh in 1931. They were registered with Mary being shown as Mary Rigby, formerly Regan. All were born at 144a Brownlow Hill, except Hugh, at Walton W H, as Brownlow had closed by then). the polite address for Liverpool Work House. I can't find a suitable match for her death either.

Can anyone help with any further details of Robert Rigby and Mary?

Robert gave his occupation as labourer at oil seed cake mill for the Birth registration and 2nd marriage in 1911, but at the time of the 1911 Census (April) he was a "guest" of His Majesty in Walton Prison. He was obviously out by October and December but I can't find any concrete evidence of him after that. There were no children registered to them until my Dad in 1918 which is unusual for those times, and without any reference to Robert or Rigby, I wonder who my Dads father actually was!

For what it's worth, the witnesses for their 1911 RC marriage were Michael Doyle and Elizabeth Pierpoint; this couple actually were the immediately preceding marriage record, with Robert and Mary as their witnesses, and both gave Prince Edwin Street as their address. Michael also described himself as a labourer at Gossage Oil Mill, so I assume the two may have worked together.

Any help welcomed!!! Can anyone find Robert for me?
Thanks in advance, Kevin