You'll need to to assign a Permission Profile for each administrator, then attach that Profile to the relevant Policy Layer (part of the overall Policy). Here are the general steps:
1| For each Administrator define a different Read/Write Permission Profile (even if the actual settings are identical).
2| Define two Policy Packages - one for each Security Gateway
3| The Policy Package is made of the specific Policy Layers, so assign each one with the relevant Permission Profile:
Menu > Manage policies and layers > layers > Access Control > Select the Layer name belonging to the Policy > Edit > Permissions
4| Add the relevant Permission Profiles
The end result is two policies that can be changed only by the relevant administrator.