Thank you AllanUK!
There are two Hollymount Cottages taken up in the 1911 census, both small dwellings with only 2 rooms housing families of 3 and 4 persons. In both cases the enumerator gives the address simply as "Hollymount" as does one resident, George Gilroy. George notes under number of rooms: "Cottage: two rooms". The second resident, George's next door neighbour, Robert Todd, gives his address as "Hollymount Cottages".
The cottages appear to be situated next to the main house. The first section of which now has dwellings of 2-4 rooms numbered 2 -12. The next 9 dwellings are given the address Hollymount House though some of the residents write Hollymount Hall.
I think you are probably correct in assuming that they belonged to the house and I believe the first set of dwellings may have been situated in the rear part of the house while the second set were in the front part nearest the gardens.