David Smith, born 1886, Alford, was the illegitimate son of Betsy Cobban and one David Smith, farm servant.
George Sinclair Cobban appears to be the illegitimate son of Ann Cobban, domestic servant (presumably a sister or other relative of Betsy Cobban). He was born in 1890 in Tullynessie. I think the George Sinclair, aged 70 in the 1901 census must be a transcription error, since he would have been 10, not 70 - but a check of the original census record may confirm this.
Now there was a Betsy Cobban born in 1860 in Alford to Walter Cobban and Ann Dyker. There were two Ann Cobbans born in Alford - one in 1871, and Ann Dyker Cobban in 1875. One presumes Ann Dyker Cobban is the sister of Betsy - but that would have made her around 15 when her son was born (which might explain why he is still with his aunt in 1901). A check of the records on Scotland's People will confirm this one way or the other.
Ruth