I have 3 objects (A, B, C). B have master-detail relationship to object A(master). Also object B have lookup on object C(parent). On layout of object A I have related list of records of object B. I need to show some fields from object C on this related list as if I have them on object B. What is the best way to show them? (I can't change relatioship between B and C to Master-Detail)
I think your best bet is to go for formula fields.
If you need to display some fields in A from C, then create a pair of formula fields in B object such as
C__r.My_Field__c and add them in A's related list, that way if you ever need to change the fields you want to display, it's just editing a quick formula field.