The Grants are a hard family to get info on :)
The only information I have is Peter was born in Finch, Stormont Co, Ontario Canada July 25,1844 (died Aug 20, 1935), and married Francis Britton in 1871. Their children were : Margaret, Uriah, Duncan, Peter, Frances, Maud, Daisy, Lily, Frances Willard, John, Angus, and Isabella.
From my research, the Grants emigrated to Canada in appros 1833 from Scotland. My uncle says it was Glenness, but there was no such name. We assume it is GlenNevis.
Yes, I understand Margaret and Duncan Grant are both buried in Laughing John Cemetery, which I think is the MacMillan Cemeter Lot 19-1 Finch Ont Canada.
Duncan's father was John Grant, and his mother Elspet MacDonald (only info that I found that matches. Margaret (Peggy) MacMillan's parents wet Margaret MacMaster of Corriebheg, and Angus MacMillan of Callich. (these I am sure).
My understanding is that Peter immigrated to the US. I am assuming you are also in US?