just wondered which is which! i always called both my grandmas "grandma" as i dont remember ever being with them both together and if i was referring to one i'd use their surname after "grandma" to indicate whom i was on about. and both my mum and boyf's stepmom both call themselves millie's "grandma". but is there a set way who's who (eg. mums mum is nan and dads mum is gran) or do u just choose?