DI Natalie Chandler of 'Law & Order: UK' may have met her husband through connections at work: his older brother could have been her mentor in the police department.
He may have been a higher-up in Scotland Yard who had a son named Joseph who followed his father into the same line of work. After his father's death, Joseph Chandler quickly became a Detective Inspector with a fast track for promotion when he landed his first murder investigation in late 2008.
As it turned out, that murder investigation tragically expanded as it became apparent the killer was emulating the historic 'Whitechapel' murders of Jack the Ripper. It was all DI Joseph Chandler could do to keep control of the case when his superiors were undercutting his authority in order to protect their own positions.
So the suggestion is that DI Natalie Chandler was the aunt by marriage to DI Joseph Chandler. And to protect each other from charges of nepotism and favoritism - and to keep each other free and clear of their professional problems - they most likely steered clear of each other within the department. This would be why we never saw the two of them together in each other's TV series......