To me it looks like half brother and sister have got together, perhaps not knowing they are related.
In 1881, Winifred Lockhart, 8, Niece, born Milnethorpe, is residing with George and Catherine Leech, in Salford.
In 1901, Robert Lockhart, nephew, 24, is residing with Catherine Leech. Both Winifred and Robert have a mother by the name of Helen Forster.
Common link to me is Catherine, both their aunt.
Tom