Sorry about the delay in replying.
The Articles of Marriage are here: lawsonsiom.freevar.com/Marr_cont/_mcon-index.html
These were transcribed by Tom Corteen, who was usually extremely accurate, and he gives different parents. However he wrote this before we had the benefit of the IGI, and I think he was just going by Margaret's age. - So your couple is probably correct as her parents, and Margaret bapt on 24 May 1807 Lonan, Father: WILLIAM KNEAL, Mother: ANN FARAGHER [IGI].
"Ann Kneale of the parish of Kk Lonnan" widow, was alive when the deed was signed in 1828, but I can't see her burial in Lonan: www.iomfhs.im/lawsons/burials/kneal_a.html
I thought she might have moved to Maughold with her daughter, but I can't find her there, either. Do you know when she died?
This William has a wife Ann: www.iomfhs.im/lawsons/twill/1818_019.html but no daur Margaret is mentioned in the will.
The other possible will for Margaret's father: KNEALE, William 1820 Lon A 1 0106242, is not transcribed on Brian Lawson's wills database.
Do you have this will, in that you gave this date for his death? If so, would you provide a transcript please? I can give you the Corteen details, if of interest.