Elan's Secret Plan

[Winter]

Could it be that Elan tries to bring in his mother somehow against Tarquin?

He got his "I got it!" when Roy was talking about "finding good in family" and there's only one other good person in Elan's family.

We also know that Tarquin was not the one who left his mother in the first place. We know Tarquin is a family-man who loves Elan, hates that he has to hate Nale for Nale being such an ass, who never made more children beyond his initial family.
We also know that Elan needs Durkon. For what? What can the dwarf do?
It's not that much that a cleric really can do in regard to "advancing secret plans", but he can cast sendings at people.

I doubt Elan would call in Ian Starshine for something, as he really has not much to do with Tarquin, unless he means to use Starshine's Opposition to Tarquin in some way but it seems unlikely Elan would see him as Racing Horse to bet on.

No, I rather think Elan will call (and bring in) his mother for help in hopes she does have some leverage over Tarquin. Also note that Elan's plans do not have to make a lot of sense to begin with and are often more fueled by Hope than actual Good Ideas.