There is a strange problem in Field Access in SD sp 20. I have folder structure like
Parent Folder Child-1 Child-2
When I set "Actual Finish" to Write Access for a related role and View for Child-1 and Hide for Child-2 folder. SD sets access rights same for all the folders. What I do last change in any of folders affects others.
It seems that I misunderstood you, I took "folders" literally as folders and not as role with children roles.
If Role A, contains Role B, then by design sd will use cascading access. What I want to say is that if Role A has a field read only and Role B has a field read write, since Role A includes Role B, whoever has Role A will have read write access to the field.
I faced a similar challenge once. Here we have some fields that must be ro by all roles but it was annoying to do this for every role.
So I created a basic role that is included in all roles and I give there the access I like. Then at the parent roles I just make all fields "view", so if both parent and child have "view" the account will have read only access. When the child role is "full access" then the account has full access.
In your case, Parent Role will have all the rights that both Child-1 and Child-2 have and in case that Child-1 and Child-2 have limited access but Parent no, then the account using parent role will NOT have limited access.