Griffith-Valuation see
http://www.askaboutireland.ie/griffith-valuation/ Balloo townland is the closest townland to Ballygrainey to contain a Robert McKee in 1863, the detail shows Robert McKee of Balloo/Ballow map ref 5Ab has just a house valued at ten shillings pa . the landlord is Mary McKee who has 3 acres and a fifteen shillings house offices and land 3 acres map ref 5A a, 5B the map shows 2 buildings marked 5A we are within the boundary of Balloo house so perhaps servants to the estate.
using the controls on the map the area is now redeveloped the homestead would be about where 2 Rathgill Glen Bangor currently stands see google street scenes within google maps
successors to the property see PRONI valuation revision books
https://www.nidirect.gov.uk/information-and-services/search-archives-online/valuation-revision-books the sources are
VAL/12/B/23/7A (1866 - 1871)
Robert McKEE takes over from Mary McKEE the map ref remains 5, 1867 robert name struck off in one entry
VAL/12/B/23/7B (1866 - 1871) couldn’t find Balloo
VAL/12/B/23/7D (1872 - 1882) found Balloo but no mckee
VAL/12/B/23/7G (1883 - 1893) no trace
So speculation Mary McKee is the mother of Robert McKee
church records from Ros Davies frozen website
https://web.archive.org/web/20170312145901/http://freepages.genealogy.rootsweb.ancestry.com/~rosdavies/Ballygrainey Presbyterian Church. This congregation was an offshoot of 1st Bangor in 1828 as the population was expanding.[ so earlier records might exist there] .This meeting house in Ballygrainey townland is called 'Bethel' and was built in 1837 ...It's where the six roads meet.
Records from 1838; North of Ireland FHS (
www.nifs.org) has baptisms 1838-1949 & marriages 1845- 1949 & burials 1861- 1999 ; the Presbyterian Historical Society, Belfast has Session Minute Books 1862–1972; PRONI MIC1P/230/6;MIC1P/407- Baptisms, 1830-1940; marriages, 1838-1912; deaths, 1861-4, 1877-1951 and 1962-74; marriage notices, 1879-1906. ; no graveyard;
References; HCPCI p56; TU p 108;DR; V 7 p 20 OSM; GIC; PE; GIPR; HCPCI p35
the children
Robert Houston Mckee abt 1843 a Robert mckee b 1844 in down
www.ancestryireland.comJohn Mckee abt 1845 if 1846 possibly listed
www.ancestryireland.comThomas Mckee abt 1847 possibly listed
www.ancestryireland.comnotes from ros davies frozen website
Ballygrainey / Ballygreny a townland of 700 acres; 3km SE of Bangor
do have a look at her surname databases if uyou don’t know her website
I did not check familysearch.org or emerald ancestors websites
good luck onwards