The Will thing is awkward. When my mother was widowed she had a whole "poor me, my family have abandoned me" narrative, with just about everyone: neighbours, priest, solicitor. Part of it was early dementia which meant she was agressive and distrustful. But also because I was expressing my concern that she was not coping on her own and encouraging her to move. She also tried to play my brother and I off against each other, so he would phone saying that I was "interfering" and that I visited too often. (Someone who had no fresh food in the flat, could no longer use the bath, had not done a tax retun since my dad died, and whose heating and washing machine did not function.)
I know she tried to change her Will, as there as bits of incomplete correspondence with the Solicitor suggesting she missed an appointment to do so. (Because...err...she had little memory.) Much of the rest of the correspondence has gone, I suspect because she woud not have wanted me to see it, though what there is is very spiteful about me and my brother.
So I am essentially managing what will be a large estate for an unknown recipient. The POA-ship requires me to manage this actively. I cannot recharge any of my legal expenses, though obviously would like some advice. And whoever is the beneficiary will be able to go back what will be two decades, and question management decisions and costs and expenses. (And from what I have heard the big corporate charities can be aggressive.)
In the end I can only do what is right and decide that I have no automatic entitlement to my parent's money.
A friend was in a position closer to OPs, though her FiL had a significant estate and a recently acquired girlfriend three decades younger. She used a Private Investigator who uncovered the girlfriend had a seriously murky past. It was sad really as the FiL was head over heels in love, but when confronted with hard facts, had to accept he had been played.