Are your friends increasing and decreasing the same cell on the spreadsheet?
If so, they can end up stepping on each other's work.
The way to work around this is to add an extra sheet, to get two sheets:
- a summary sheet with the total for each item being tracked, and
- a detail sheet with one row for each increment(+1) and decrement (-1) to that item's total.
Using this system, each person only adds rows to the detail sheet independently, and do not update the summary sheet, avoiding conflicts.
Study the Google Sheet's @IFSUM functions to see how to do this.
Sample detail and summary project: