Grandma didn't know how to manage money so she co-mingled her funds somehow with her brother to invest. Her brother re-married and then died about 3 years later. He got swindled by his new wife's lawyer/financial advisor and made a new will on his deathbed and left everything to the new much younger wife and step-kids... including my grandma's money since they had joint accounts of some sort (don't know all the details)
Other Lessons:
1. Lawyers/financial advisors can be snakes (not all, but shitty ones are out there and they don't announce themselves).
4. If you want to give money to family members or causes you care about, you should consider doing it BEFORE you die.. stuff can get messy once you're gone. My grandpa is probably rolling in his grave knowing that all of the money he saved his entire life ended up in the hands of people he never met or cared about and they proceeded to spend it on vacation houses, new cars and other shit he didn't care about.
One thing I've learned about lawyers, is that their job is not to be "fair", it is to represent the interests of the person who hires them. Brother's new wife's lawyer may have done his job perfectly, which was to draft and get executed a new will that the brother legitimately signed for his new wife, deathbed or not. The lawyer may in fact have had no idea that Grandma had passed money to the brother in joint accounts, and who knows if the brother thought to bring it up at that point. I would say new wife was not very fair if money was not returned on being shown it was originally Grandma's, though.
Something I did learn from some experiences like that is when helping elderly relatives manage their financial affairs, regardless of the reason for doing it, be very careful with how accounts are set up. There can be good reasons for setting up joint accounts, but a better idea may be having power of attorney on an account of theirs. The latter is more of a pain, but prevents a lot of problems, such as IRS or lawsuit attachment of a jointly held account.
I can provide a story regarding your item 4, though. My FIL's half brother, H., was a frugal investor his whole life, and had saved close to $1M by the time he passed away. He left almost all of it to his long time GF, they had been together 20 years or so. Not a problem so far, he had no children or other closer relatives than my FIL. She was around 90 when he passed away, and a nice person but not very financially competent, so her family was managing her affairs. My FIL was executor, and when I was helping my FIL clear out H's apartment we came across several rather aggressive letters over the years from said family begging for money for one self inflicted disaster or another, apparently they knew H had a fair amount of money saved, and were of the mindset that if he had money, and they didn't, it was his obligation to provide them some so they could buy the things they wanted. I mean, why would anyone have money sitting around idle?
They were bugging my FIL for disbursements from the estate within a month, and wanted all the investments sold and turned into cash as fast as possible. As soon as they got it, the long time GF, their parent, was put into assisted living (to be fair, she needed it at that point) and I'm sure they spent the money H had spent a lifetime accumulating within a couple of years. Its just like winning the lottery. . .