Hi, all the below would need to be confirmed by certificates but could be your John.
First marriage to Mary Elizabeth Davies JQ 1910 Pembroke 11a 1794. There is a transcription error as Mary Elizabeth appears on ref JQ 1910 Pembroke 11a 1704
Mary can be found on 1911 census as married with two sisters, and has been married for less than one year. John, being a "fisherman" is probably out at sea.
They then have 3 daughters who sadly all die in infancy. Elma 1913-1913, Alice Elizabeth 1916-1916 & Dora 1916-17. Gets worse I'm afraid. Mary Elizabeth his wife dies aged 30 in 1916 (probably from childbirth complications with Dora in 1916)
John is then on Pembrokeshire Electoral registers from 1929-1960 onwards living with Eliza/Elizabeth whom he marries in 1948. His son John born 1926. Cannot work out at present why mmn is Hart. John junior goes on to marry Audrey F V Evans in 1945 & 5 children are born to them. They can all be found on freebmd. John senior dies 1961 and John junior in 1996. I will continue to try and find out where the mmn is Hart comes from.
Possibly Eliza Ann HART MQ 1888 Pembroke 11a 998, hence John's juniors mmn.
John
