How to Decouple Inheritence in Objective-c

We have a Base class A, and two derived classes B and C. We wanted to build separate framework for B and C. We didn't wanted to copy A to B as well s to C to create the frameworks.

We have implemented custom KVO, this Custom KVO class is super class of A. It would read all the modified properties in a object and post the messages to concerned objects.

I tried

1. Making A and B to a "Has a relation", but when this custom KVO was asking for all the modified properties it is only able to read A's properties.
2. Tried using class_setSuperclass, it is also deprecated.

Suggestions are required.

Thanks, K.Prabhakar