A CHAINED GENITIVE is when the possessor already includes a genitive:

He is Mick

This is Mick's brother

Mick's brother has a pen

This is Mick's brother's pen

It is the mummy's turn to wash the dishes.
It is the mummy's friend's turn to wash the dishes.
No! But I've got to howl at the moon!
I have to walk around and then say, "Aaaaaah"
It is the mummy's friend's bat's turn to wash the dishes.
But I don't even have hands!
Not a problem.
It is the mummy's friend's bat's flea's turn to wash the dishes.
Typical!