At the end of George St. in Mitchelstown/Brigown is St. George's Arts and Heritage https://www.saintgeorgesmitown.com/ . Today its being renovated as a museum but it used to be a church of Ireland site. In the 1780s RC burials would also have taken place in these sites. The graveyard was recently surveyed as part of the Ballyhoura Development Historic Graves project https://historicgraves.com/graveyard/brigown/co-brgw . From doing a name search I can find 2 Donovan's in this graveyard (and in graveyards surveyed in the surrounding area). There are a few Hallorans recorded in neighbouring parishes. To search family names go to https://historicgraves.com/graves-search . Note that only legible headstones are recorded and not all graveyards are surveyed yet so just because you can't find someone on historicgraves, it doesnt mean they are not there somewhere!
I hope this information is helpful and it will help to refine your search. Getting in touch with St. Georges would probably be a good place to go from here.