It is down to probability mathematics.

A child raised by one or more depressive parent will be more likely to be depressive than a child not raised by a depressive parent.

There is the inherited brain chemistry and cerebral architecture and there is the fact that being raised by someone who is depressive is in of itself depressing.

That doesn't mean that every child born to and raised by depressive parents is going to be the same it just makes it more likely.

In Luke and Leia's case they haven't been raised by the same parents let alone the one with the magic wish power.

So the only source for this family strength that Ben and Vader hopes to use against the Emperor and Palpatine fears is genetic.

Anakin and Vader are practically two people occupying the same body.

Vader wants Luke to give him the edge he feels he needs to kill the Emperor and replace him.

Anakin wants to be with his family.

Anakin's latent love of family kills Vader and the Emperor.

And if Palpatine is so smart to foresee and fear that affection why does he force a fight between the two in a room with a bloody great hole in the floor leading to a bottomless pit?

I can swallow the hubris that would guide him to actually turn up to the station in person as per his own deliberately leaked intelligence and not send a decoy or clone but that's just taking the piss.