Sometimes classes become far too intimate and spend too much time delving in each others'private parts. We may not be prudes when it comes to people, but we think our classes should follow strict, puritan rules.
Overintimate classes need to be broken up as lovers were in ancient days. Use Move Method and Move Field to separate the pieces to reduce the intimacy. See whether you can arrange a Change Bidirectional Association to Unidirectional. If the classes do have common interests, use Extract Class to put the commonality in a safe place and make honest classes of them. Or use Hide Delegate to let another class act as go-between.
Inheritance often can lead to overintimacy. Subclasses are always going to know more about their parents than their parents would like them to know. If it's time to leave home, apply Replace Delegation with Inheritance.