The William Connell who married Elizabeth Smith in Mallow in 1858 was a butcher, residing in Mallow, and the son of another William, also a butcher. Your ancestor who died in Drumnadreagh was a farmer, according to his death certificate. Farmers didn't move around much, nor are they likely to have been working 300 miles from home, as a butcher in Mallow. I don't think the 1858 marriage is the same family. (I also see a death for a William Connell, butcher, in Mallow on 22.12.1878). Likewise I see you have 3 children born in Ballymena,Lisburn & Antrim town. That's not imposible but would be very strange for a farmer.How certain are you that you have the correct events? I would have expected his children to be born on his farm. Have you checked the local baptism records for Presbyterian churches near Drumnadreagh? (I assume the family was Presbyterian. If the church has records for the 1820s they may well not be on-line. There should be a copy in PRONI though). Jenny McConnel appears to have married in Ballycarry Presbyterian so that may be the family church. Their baptism & marriage records start in 1832.
William McConnell's will is on-line on the PRONI site.Dated 1881, it mentions sons William & Robert (still alive) and sons James & Thomas (both deceased). The residual legatee was Thomas's wife Catherine, who was also one of the executors.