The 1881 census has for only McCaa family on Island
Lonan MC CAA Robert Gretch Voar Farm House Head M 44 Farm Steward Of 70 Acres --- born Scotland
Lonan MC CAA Elizabeth Gretch Voar Farm House Wife M 37 --- Lonan IoM
Lonan MC CAA Robert Gretch Voar Farm House Son U 15 Scholar Lonan IoM
Lonan MC CAA Elizabeth Gretch Voar Farm House Daur - 14 Scholar Lonan IoM
Lonan MC CAA Alexander Gretch Voar Farm House Son - 12 Scholar Lonan IoM
Lonan MC CAA John Gretch Voar Farm House Son - 10 Scholar Lonan IoM
Lonan MC CAA Janet Gretch Voar Farm House Daur - 8 Scholar Lonan IoM
Lonan MC CAA Annie Gretch Voar Farm House Daur - 6 Scholar Lonan IoM
Lonan MC CAA Edward Gretch Voar Farm House Son - 4 Scholar Lonan IoM
Lonan MC CAA Mary Gretch Voar Farm House Daur - 3 --- Lonan IoM
Lonan MC CAA Andrew Gretch Voar Farm House Son - 2 --- Lonan IoM
Lonan MC CAA Aanes(? Agnes) Gretch Voar Farm House Daur - 8 --- Lonan IoM

the 1881/2 directory has McCaa, Robert, steward to James Williamson, Gretch-voar
father robert buried Lonan14 Aug 1904 age 66, Elizabeth 9 Apr 1893 age 49 and an Alexander 3 Jul 1904 age 35
his son Robert would appear to have emigrated to USA as I have a photo of him in Mona AFC in 1908 (see www.manxnotebook.com/exans/prt_1909.htm)
a J McCaa is also noted as trustee of Mona's Mutual Benefit Society of Cleveland in 1916.

I have no other ref but it might be worth checking if any of the daughters married and remained on the Island from http://www.lawsons.ca/marriages/m_mar.html there are marriages for Agnes McCaa (not sure to whom) in 1913 + Ann to Robert Bryson NEWELL in 1897