Although there probably aren't church records of burials as in a formal burial register such as Church of Ireland keeps there are a few other things to ask the church about.
1) graveyard map? this will perhaps show that there is a family plot even if no headstone erected
2) sexton's notebook? notes kept by grave digger often show date of burial and name of deceased
Ministers are usually from outside the area, may not have been there long, etc. so the best person to speak to might be the person in charge of the graveyard (convenor of graveyard committee if they have one) or Clerk of Session