Hey Neil,
Thanks for your report! The best way to accomplish what you are wanting to do is to use the Position Grid Snap option. There is a list of Preset Grid Sizes, but there is also a User Defined list.
The User Defined list can be customized by going to Edit > Editor Settings > General > Preferences > Snap (or simply search for “grid” in the Preferences). Here you can expand Grid Sizes and change any of the sizes to the number you want.
Once you have modified this setting, you can then go back to the Position Grid Snap option and see your new User Defined Grid Size.
Each person working in your project will need to make this change in their Editor Preferences, but that should have everyone working on your desired Grid Size.
Please let us know if you have any additional questions!
Thanks!
-Steve