I am confused, it’s easily done.
The certificates don’t match. The birth certificate is for a girl surname VENI but the marriage certificate shows the bride Helen BROUGHTON and the groom Robert VENI.
James VENI deceased is named as grooms father not John.
According to the certificate Helen made her mark rather than signed.
The certificate is only a copy, so it is quite possibly for whoever transcribed the original to have made a complete mess of the facts.