I disagree - someone is taking advantage of your parents - that gives you the right to interfere!
In our family, it is my FIL who pisses us off over and over again. He and MIL divorced some years ago, so when we had to tell him that she had died (of cancer) I didn't expect him to be grief-stricken, but I am very angry that he has not once asked if dh or his brother are coping with the loss of their mum, after a long, painful illness that was stressful for all of us - especially BIL who lives near where mil lived and therefore did a lot of the care and supporting during the years of her illness, and who now has a massive hole in his life.
He has, however, asked all of us several times, what is happening to the money MIL was paying him (part of the divorce settlement - to do with the house), and has a list of things he wants from the house - despite knowing that he has no rights to any of it, following the divorce. Some of it is sentimental stuff, and I do understand why he wants it, but fgs, FIL, we have only just buried her, please have a bit of sensitivity.
I swear, if he rings me again, with more of this crap, I WILL be telling him what I think! even though you could argue it is not my responsibility - he's not my dad - but I care about dh and his brother, and I WILL stand up for them!