I think you need to check out the marriage of Peter Le Prevost and Nancy Sarre to check Peters fathers name.
There are 2 Peters born in Guernsey around the same time.There are 2 trees on Ancestry one has Peter marrying Nancy Sarre but his parents are down as John and Elizabeth Le Prevost
The other has Peter marrying Nancy Sarre but his parents are down as Peter and Mary Le Prevost.In 1841 and 51 Peter is with his mother and siblings.
One obviously has the wrong parents.
Also in the 1881 census when married to Nancy his date of birth 1842 in Catel,Guernsey which matches with the 1851 census below with parents John and Elizabeth?
1851 St Peter Port,Guernsey
John Le Prevost,Head,30,Carpenter,St Saviour Guernsey
Elizabeth Le Prevost,29,Catel,Guernsey
Peter Le Prevost,Son,9,Catel,Guernsey
Thomas Le Prevost,son,7,Catel,Guernsey
Mary Ann le Prevost,Dau,2,Catel,Guernsey
Eliza? Mc kane,Visitor,un,30,Tailor Journeyman,Catel
Abraham Mc Kane,Visitor,un,25,Shoemaker,Catel
Judith Mc Kane,Visitor,22,Dressmaker,Catel
Welsh lady