Looking at the 1851 census index there is:
Nicoll Alexander age 51 b. Arngask, PER, Living in Orwell
Nicoll Janet age 28 b. Forgan PER, Living in Orwell
Looks as though they had at least 4 of a family:
Ann age 15,
Jane age 8,
John age 26,
Peter age 13.
Could these be your folks?