The tithe applotment records only list folk with land, so they are not a complete survey of every house in the townland. So where you have folk without land or sharing property, they won’t be listed in the tithes. So there might have been 5 or 6 Davidson households there in 1827, or as you say, some property might have been split off, though that wasn’t a terribly common practice for farmers in Ireland. (Most farms weren’t really big enough to be split much).
1831 census for Drumrot lists 6 Davison households (nos 15 – 19). 2 households together in no 18. That they were all consecutive would suggest they were very close to each other, and so probably related. The numbers were the enumerators private numbering system and don’t relate to any other set of official records.
House 15 was headed by William who had 3 males & 2 females plus 2 servants. All were Presbyterian save for 1 servant:
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinsholin/Lissane/Drumrot/15/
House 16 was headed by Ellen whose family consisted of 4 males & 3 females, plus 1 female servant. Again all Presbyterian save for the servant. Ellen was listed as Wd, ie a widow (see the original image).
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinsholin/Lissane/Drumrot/16/
House 17 was headed by William junior with 2 males & 3 females and 1 servant. All Presbyterian save for the servant,
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinsholin/Lissane/Drumrot/17/
House 18 was headed by Robert & George with a combined total of 4 males & 1 female servant. Again all Presbyterian save for the servant. Noted as 2 separate households, so probably either Robert or George had part of the property to themselves.
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinsho…
House 19 was headed by Jane whose family consisted of 3 males & 3 females, all Presbyterian. Jane was a widow (see the original image).
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Loughinsho…
In general, in a rural area, a household with servants was a farm, so it looks as though all but one were farms. And the last might have been a farm too.
Ignore Wilson Blair in house 19. That’s a transcription error and he actually lived in a different townland.
If you have not already done so, it’d be worth searching the Registry of Deeds records for Drumrot to see if any deeds were registered there for the family. You might get a 3 lives lease from the 1700s which often helps connect and sometimes age families. (They are on Familysearch. A bit fiddly to work with till you get to grips with the system but sometimes very helpful).
The PRONI e-catalogue has a number of leases, dated November 1820 eg:
D3632/B/25/1 Lease of a holding in Drumrot from the Drapers' Company to Eleanor Davidson.
Eleanor is probably the Ellen in the 1831 census, so that tells you she was widowed by November 1820.
I see additional leases for Jane & for William dated Nov 1820, Elizabeth Nov 1827, Andrew, George, William jr, William senior all dated November 1854. In 1862 there was a:
Bargain and sale, from William Davidson to George Shannon, of the townlands of Coltrim and Drumrot, with a declaration of the receipt of purchase money.
The above leases are not on-line at PRONI but you may find them in the Registry of Deeds records on Familysearch. PRONI has original copies and they have also put them on a microfilm - MIC 617/13 which is probably part of the Salters Company papers. Personal visit required to view them.
If you know what church the family attended, you could search their records. Nearest Presbyterian church to Drumrot looks to be Claggan. (Presbyterians didn’t always attend the nearest to where they lived). Claggan has baptisms & marriages from 1846 onwards. Presbyterians generally didn’t keep burial records but worth checking local graveyards as being farmers they are more likely to have a gravestone. There’s a copy of the Claggan records in PRONI. Not on-line anywhere so far as I am aware.
Londonderry Sentinel of 3rd April 1841 has this:
WHITE-DAVISON – On the 25th ult., by the Rev. Dr. Barnett, Presbyterian Minister of Moneymore, Mr. Thomas White, Anahavil, to Margaret, youngest daughter of the late Robert Davison, Esq., Drumrott.
So that tells you Robert Davidson died sometime between 1831 and April 1841. Also, tradition was to marry in the bride’s church which in this case was Moneymore Presbyterian. So perhaps that was the family church? Moneymore 1st Presbyterian church has records from 1827 onwards. Again there's a copy in PRONI. It probably also tells you that these families were quite well off by the standards of the time. Only gentry and more significant farming families put marriage notices in the paper at that period.
You can use the Valuation Revision records on the PRONI website to follow Griffiths Valuation forward to see changes of owner/tenant or size of property up to 1929.
There look to have been 2 Davidson households in Drumrot in the 1901 census:
http://www.census.nationalarchives.ie/pages/1901/Londonderry/Moneyhaw/Drumrot_1/
http://www.census.nationalarchives.ie/pages/1901/Londonderry/Moneyhaw/Drumrott_2/
I see a death for Andrew Davidson in 1887 aged 83, son James was the informant. Possibly his wife Nancy in 1892 aged 72. Daughter in law Sarah was the informant. If you search the statutory BDMs for the Magherafelt area on the irishgenealogy site, you may find some more.
Probate abstract:
The Will of George Davison late of Drumrott County Londonderry Farmer deceased who died 14 April 1862 at same place was proved at Londonderry by the oaths of William John Hutchison of Ballynenagh and Robert Brown of Ballyeglish both in said County Farmers two of the Executors.
Above will is on-line on the PRONI wills site. In it George leaves bequests to his brother James’ children in Moneyhaw. Children were George, Smyth & Mary Davidson & Jean McCan. James wife was still alive (1861). It mentions his sister Jean Miller of Lisbouy, her children Jean Erwin, Susan Young & Margaret Miller. There’s a bequest for George Davidson, son of his next door neighbour, William (so not an immediate relative). Also George mentions his wife Sarah.
Being Presbyterian, living in Co Derry from at least the early 1700s and having a common Scottish name, all point to the family being descendants of the many Scots who settled in that area in the 1600s.