Hi Sarah,
I don't have access to the 1841 Cencus but I had a look in the British Vital Records to see if I could find anything more about your William Handyside.
It seems he was an only child (or the only child registered) to John Handyside and Mary Pollock as there were no other siblings listed.
Other details: Date of birth 22nd April 1827
Recorded in: Edinburgh, Midlothian, Scotland
Collection: St Cuthbert
Anne