First of all, when we you define a method again, you are overriding it, which means only one version of the method is called. No method will be called before the other.

Odoo will look into your __openerp__.py. It will check the 'depends' list value. It will look for the method your are overriding in the modules in the 'depends' list.

Odoo will try to find the method in the first module in the list, if not found it will look into the next module, and if not it will look into the 3rd one, etc ...

So, if method B override method A and method C overrides A as well, you need to add the module name of the method A in the 'depends' list before the module name of method B. 

On the other hand, if method B overrides method A, and method C overrides method B, you need to add the module name of the method B in the 'depends' list before the module name of method A. 

Hint: The module name is the same as the folder name in [Odoo home directory]/addons folder