Claire
Some time ago I was aware of Swans and Darlings cohabiting on various census returns.
Ann Swan, 1803 from your your search had a brother Thomas,1811. Together with his wife, Isabella, they appear on the 1881 census for Durham, Hedworth, Monkton and Jarrow at 1 Staple Row along with William (H?) Darling and the relationship is given as cousin.
That's the first time I've been able to pull the Swan/Darling trees together in any credible way.
Good work team!! Now need to chase Wm Darling back and see where he fits in to the picture.
Richard