I have just been working out why I cocluded that Louisa who married James Stevens was the daughter of Stephen Whitehill.
When Louisa died her executors were William Warden Bell nephew and Charles Forbes Shephered grandson. I believe William Warden Bell was the son of Sarah Whitehill and Alexander Bell?
Do you have Stephen Whitehill's will? That mentions that his 2 older daughters Mrs Bell and Mrs Torin have his younger daughter Louisa under their care.
I wish I could find the marriage of Louisa to James Stevens. It is very frustrating! Their youngest son had the middle name Whitehill and the name was used again for a grandson, Malcolm Whitehill Lewin.
Barbara