OK, I've got it - the first three portrayed their own grandmothers and the other two only portrayed their own mothers:
Geraldine Chaplin in Chaplin
Tencho Gyalpo in Kundun
Chelsie Preston-Crayford in Home By Christmas
Gloria DeHaven in Three Little Words
Jetsun Pema in Seven Years in Tibet
I have to say that I've only ever heard of two of those ladies (Chaplin and DeHaven) and have seen none of those films, but Google and Wikipedia delivered the goods.
I'll have to think of something to ask.