Hi again Paul

I don't think he would have been able to marry at the age of 14*:
In 1763, the minimum age of marriage was fixed at 16. Prior to this date, the church accepted the marriage of girls aged 12 or more and boys aged 14 or more. In addition, a dispensation on licence could be obtained from a bishop which allowed marriage at a younger age. From 1763 a person below the age of 21 required the consent of parents to be married in England.
http://www.parishregister.co.uk/history.htmI think getting the 1914 marriage certificate would give you the information that you need to go backwards. However, although it would be more expensive, if you are unclear, it would be worth getting both your father's marriage certs and his birth cert.
We have to be careful about mentioning people who may still be alive, so it isn't possible for us to help with your half siblings.
Regards
Gadget
* Added - unless he gave the wrong information about his age to the registrar/minister/priest
Ps - I mis-read your post - thought you said that yours married at 14
