Oh, I love posts like these

but unfortunately I also have to be careful as it is living people

The Salvation Army Family Tracing Centre is absolutely
BRILLIANT and suggest you speak to them immediately. They are expert researchers with over 100 years' service in tracing long lost family or relatives.
An alternative is: have you tried to find a marriage for a
(*) in Sheffield? That would be your first pot of call - then you can search for children to see if they stayed in Sheffield where they had any or if they moved away.
Good luck & best regards,
Jayne.