Is my mother’s step-father, my step-grandfather? To what extent is it usual to extend the prefix ‘step’?
Can we speak of ‘step-cousins’, step-aunts and step-uncles etc? If we can it must make for considerable complication in how such relationships are defined.
Of the combining form step-, Oxford Dictionaries only says:
denoting a relationship resulting from a remarriage
Past immediate step-parents or step-siblings, I no longer find the distinction useful.
Introduce your mom’s stepfather as “My mom’s stepfather.”
Likewise with your stepmom’s sister, your aunt’s stepdaughter, and so forth.