Gerry,
I had a look for any George Holmes in the general area where Francis & Eleanor lived. This is the only marriage I could find, for a George in that area. He married Margaret Smart in 1856. He was a pensioner which, at that time, meant he had served in the army or navy. And for long enough to qualify for a pension (20 years perhaps).
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1856/09517/5449454.pdf
In case you can’t make it out, his address was Church St, Newtownards. This may be his death in 1879 (occupation discharged soldier).
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1879/06501/4872102.pdf
I can’t find anything on either Margaret Holmes (James’ sister) nor Margaret nee Smart.
James Holmes birth, marriage and death are all long before the start of statutory registration (1864 for births & deaths, 1845 for marriages). Prior to those years you need to rely on church records. Not all churches have records for those years, and of those that do, many are not on-line. So you will certainly struggle to find any record of him. Ideally you need to know the precise denomination and have some idea of where the person was born in order to search the correct records.
RC records are mostly on-line on the nli site:
https://www.nli.ie/en/family-history-introduction.aspx
For other denominations, the churches usually hold the originals but there are also copies in PRONI, the public record office, in Belfast. A personal visit is required to access them. Access to the records there is free. This link explains what records exist, parish by parish:
https://www.nidirect.gov.uk/publications/proni-guide-church-records
If you are unable to go yourself, you could employ a researcher. Researchers in the PRONI area: http://sgni.net