Hi
The Berry family plot is unmarked. However, the grave adjacent to it belonged to someone called William who died aged 10 of sleeping sickness. I know this because your grandmother was my great aunt and my gran used to take me to the grave when I was a little girl. We used to access it through a break in the wall, coming back from the park, so it is located on the opposite side of the churchyard from the main road.
I attended your grandmother's funeral too. It wasn't held at St Cross and I wasn't aware that she had been interred in the family plot. My gran, Lily Anderson (nee Berry), your grandmother's sister, told me there were generations of her family in that plot, but they'd never had a headstone.
I went looking for it myself today. The park and location has changed so much and I couldn't find it, although I did find a newer headstone marking the grave of Thomas and Mary Jane Berry. This isn't the grave I remember though. Hope this narrows down your search.