From what I've seen of Sumiko (and I've only seen as much as you, methinks), I wonder what she sees in Shuuji.

Tokine may think Mama Sumimura is a lot like Yoshimori, but I think Masamori is the one who takes after her, based on this.

All the cunning is already passed on to the first child and nothing is left for the younger siblings?

Sumiko and Masamori are mostly away from the house, but people just have to pop up at the Sumimura doorstep and bring up their names.