You mention Maria Davidson McKinley. However the burial records just record her name as Maria Davidson. I don’t think she was named McKinley.
Belfast Telegraph of 11th Aug 1980 has a death notice: “Davidson Maria - August 9 1980, at hospital, late of 7 Jocelyn Ave, dearly beloved friend of John & Hessie. Funeral Service in Wilton’s Funeral Home. Woodstock Rd tomorrow (Tuesday) at 10.15 am. Interment afterwards in Roselawn Cemetery. Very deeply regretted by her sorrowing friends. John & Hessie McKinley 13 Braeside Grove, Braniel. At home with the Lord.”
You could order a copy of Maria’s death certificate from GRONI to find out a little more about her. (Likely cost £15 sterling). And she may have left a will which should be in PRONI (when it re-opens). That’s free to view if you can go in person.
Can’t see a notice for Hessie’s death.