Kimberlee,
Yes the OC church is rather fine. It’s one of only 2 oval shaped churches in Ireland and rightly has all sort of preservation orders etc.
You say that Allan Noble senior was born in Scotland c 1811. Is there documentation for that, or is it just speculation? He could be born there. Folk went back and forth all the time, as they still do, but in general terms the main body of Scots arrived in Ireland in the 1600s. Something like 200,000 came that century (representing 20% of the population of Scotland). By the 1700s and 1800s they were leaving again for economic and other reasons. That’s not to say some didn’t arrive in the 1800s but it would be against the flow.
For a good description of life in the area in the Randalstown area in the 1830s, you could read the Ordnance Survey memoirs. These were compiled on the instructions of the Duke of Wellington (then Prime Minister) primarily for taxation purposes. So a bit like the Domesday Book. They were compiled parish by parish, and describe the inhabitants, their occupations, pastimes, habits, they analyse the various different denominations by number, and report on health, schooling, seasonal migration patterns as well as permanent migration (often with lists of names of recent migrants). And so on. A typical parish contains about 20 to 30 pages of information and some drawings. They are well worth reading if you want to get a feel for life there at that time. (It’s probably the most detailed contemporaneous summary that exists from that period).
There are copies on the bookshelves in PRONI’s main research room in Belfast. You can order a copy from the Ulster Historical Foundation. If you e-mail them with details of the parish(es) you are interested in, they’ll send you the relevant volume(s). Generally there are 3 or 4 adjacent parishes in each volume. I think they are between £5 and £10 per volume depending whether it’s old stock or newer reprints. Drummaul (the parish which includes Randalstown is in Volume 19).
https://www.booksireland.org.uk
You ask about possible descendants in Ireland today. It seems likely there could be some. William Weir & Ellen Noble married in 1857. For any children born 1857 to 1863 you would need to check the OC baptism records in PRONI but from the statutory records which start on 1.1.1864, they appear to have had William 2.6.1864, Allen 29.6.1869, James 2.11.1871, Elizabeth 20.4.1874, Ellen 13.7.1876 & Alexander 22.8.1881.
I had another search for Ellen and her family. Disregard the one I suggested earlier (living alone in Randalstown). This looks to be the right one in 1901 living near Larne with daughter Eliza who had married Thomas Pollock:
http://www.census.nationalarchives.ie/pages/1901/Antrim/Kilwaughter/Drumahoe/995068/
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1897/10469/5812597.pdf
Same family in 1911:
http://www.census.nationalarchives.ie/pages/1911/Antrim/Larne/Carsons_Street/196189/
The Pollock/Weir family are on 30 trees on Ancestry, so you ought to be able to get something from some of them. Thomas Pollock reportedly died 23.5.1958 in Larne and Elizabeth Weir died there in 1948. They apparently had 8 children who died in the usual spread of places for folk from Ireland (4 in Larne, 1 in Renfrewshire, 1 in Adelaide SA and 1 in “Australia or New Zealand.”)
Margaret Noble married in 1870 and I can see 2 daughters for her. Eliza Jane McClenaghan 4.7.1871 who married James Neill in Belfast on 30.3.1891 (she’s on a tree on Ancestry owned by Claire McMeekin, so you may get more information from her).
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1891/10656/5882741.pdf
Also Sarah Agnes McClenaghan was born in Caddy on 24.4.1874. Don't know what became of her.
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1874/03152/2155992.pdf
I’d expect Allan Noble & Jane Foster probably had a few more children than the 3 we know about so there could be others out there. Researchers in the PRONI area who might help with more detailed research: http://sgni.net
If the Noble family were living in the Randalstown area in the 1700s and early 1800s, then to answer your question I think you will struggle to get back much further than Allen and Jane. But you may be able to find other members of their family and their descendants, if only from the Ancestry trees.
Note that not all professional researchers will search for living descendants. It can be a sensitive area. (On Ireland Reaching Out we have a policy of not giving out living people’s details).