Dad said the way to your wife's heart is through her mother..

...there's more to it here.

Tonight, the sister is playing beautician to Olga.

And she's speaking to her about other men as though she is a single lady without any attachments (..whilst assuming of course that I understand zero of their discussion..).

The other evening her mother was doing the same, regarding other men.

It's repugnant.

Is Dunia's best interest at heart in these actions/discussions?

If you define Dunia's best interest as excise her Dad from her daily life, and give her over to the maternal family in order that they raise her at their pleasure & leisure.

In other words: absolutely not.