Hi, I think I see 2 possible further siblings for Sarah
Anne Eliza Bovill married Peter Pinkington TAMLAGHT UPPER (O'CRILLY) (CI), Co. Londonderry, 1850, Anne's father is recorded as Samuel Bovill, the civil record of this marriage is recorded at Ballymoney, Co. Antrim for some reason. Vol 2 page 231
Rachel Boville married James Falknor TAMLAGHT UPPER (O'CRILLY) (CI), Co. Londonderry,1859, Rachel's father recorded as Samuel Boville, again the civil record of this marriage is recorded at Ballymoney Vol 2 page 208
The name seems to have stronger associations with County Antrim more so than Londonderry.
Regards
Joe