Saintfield 1st Presbyterian church doesn’t appear to have any baptisms earlier than 1854 and marriages before 1845, so you won’t be able to expand your knowledge of the family from that source.
PRONI names index records a John Russell senior, of Tonaghmore, whose probate was granted in 1805. So clearly the Russells have been in the area since the 1700s and probably the 1600s.
The tithe applotment records for 1834 list 2 Robert Gibsons. There’s also a George Gibson in Tonaghmore. There are also 6 Russell farms in Tonaghmore, including Hugh.
Griffiths Valuation for 1863 lists Hugh Russell senior on plots 1 & 2 which combined came to 17 acres. (That farm today is up a lane off Middle Rd, Saintfield). There are numerous other Russell farms in the townland. You can follow through and see when the tenants changed using the revaluation records on the PRONI website.
Hugh senior changed to Mathew in 1870, then to Hugh jnr in 1883. His name remains as tenant till the expiry of those records in 1929. It looks as though Hugh was replaced by Hugh so no change of name is recorded.
Probate abstracts from the PRONI wills site:
Probate of the Will of Hugh Russell late of Tonaghmore County Down Farmer who died 3 May 1898 granted at Belfast to Matthew Russell and Hugh Russell both of Tonaghmore Farmers.
Russell Hugh of Tonaghmore Saintfield county Down farmer died 6 June 1929 Probate Belfast 26 March to Elizabeth Russell the widow and John Massey farmer. Effects £31 15s
There are 9 probate abstracts for Russells of Tonaghmore on the PRONI website. Where the wills are not on-line the file may be in PRONI in paper format.
There are 4 Gibson abstracts for Tonaghmore too.
PRONI have a mortgage taken out by William Russell of Tonaghmore 11th March 1884. T3555/20.
4 Russells from Tonaghmore signed the Ulster Covenant in 1912, which tells you about their political views. You can view their signatures on the PRONI covenant site.
Possibly worth searching the registry of Deeds records to see if there are any leases for the Russell farms in the 1700s and 1800s. (Those records are not on-line but can be inspected in the Registry of Deeds in Dublin. There is also a duplicate set held in PRONI. Allow an hour or two if searching them).
5 Russell households in Tonaghmore in the 1901 census:
6 in 1911:
There’s a Hugh Russell death recorded on 3.12.1875 aged 75, regd Lisburn (which would cover Tonaghmore). Don’t know if it’s your family but you might want to look at that.