What next?

Linton

Other points to note....

-if the siblings take legal advice they will not benefit from the estate paying the costs.  The step-mother's inheritance (a specified cash lump sum and the right to live in the house) are both guaranteed ahead of the siblings who just get what is left over after any legal costs and other executor's costs.

-Were any of the assets believed to have been taken by stepmother under POA held in joint accounts with her husband?  If so the contents of the joint accounts would pass to her directly outside the well.

-The siblings need to realise that they had/have 3 distinct roles, PoAs, executors, and beneficiaries.  When ever they take any actions it is important that they understand which hat they are wearing and act within the the bounds of that particular role. For example their PoA role ended on the death of the father and is now irrelevent.  Their role as executors limits them to implementing the will as written, not as they would have liked or as "Dad would have wanted"

I would conclude that step-mother holds all the cards and that the siblings need to cease antagonising her and to offer her sufficient to get her cooperation in sorting out the will.