1) I have a model A which I want to allow user group G to read, write, and create.

2) Also I have a model B which I only want to allow user group G to read.

3) There is a many2many relationship between A and B.

I want group G to be able to edit add/remove relationships between A and B. So I need the relationship field to be writable. 1) means that this won't work. What can I do?