Thank you for your question.
In your situation, there are two things to consider. The first is whether or not you become exposed to liability by reporting this situation to Jane's ex-husband and kids. The legal issue that arises here is called "defamation
." If you told the storey above in specific to Jane's ex-husband then you could potentially be sued for defamation by Mary. That being said, you could proceed to inform Jane's ex-husband or children about the situation, but first you should get them to sign some sort of non-disclosure agreement in which they promise to not disclose that you told them this information unless they file suit against Mary.
The next issue is whether there is anything that would or could result from you telling Jane's ex or kids. The answer is, not really. Although you feel that there was some bad behavior when Mary arranged to spend money and take property which belonged to Jane, because you are talking about this taking place over time, this would be a case that might be barred by the statute of limitations
. Essentially, the claim would be a claim for breach of fiduciary duty
and breach of trust
against Mary which would be held by Jane's estate. The supposed beneficiaries
of the estate might have the right to bring that claim. Again, however, this sounds like it might have taken place too long ago for there to be a claim within the statute of limitations. The other issue is that Jane's ex-husband and/or kids might not have any standing to bring this claim. You did not indicate that there was a will, but I would imagine that if Mary was actually doing all this stuff under the pre-tense of illegality, she has probably got the estate documents set up to exclude both the ex and the kids from having any benefits of the estate.
In short, you might as well tell the ex-husband under an agreement that he won't say that you disclosed the storey, but don't expect that anything will actually come out of it.
Please let me know if you have further questions on this matter.