The way I understand it- And I may be injecting my own biases into it- is this:
Grandpa Athanasios "Artie" DeMoulas and his brother started the store around 1915, and ran it for most of their lives before retiring and selling the store to their sons, Telemachus and George. From the mid-1950s through 1971, George and Telemachus expanded to 15 stores, when George died of a sudden heart attack.
Telemachus continued running the stores, while paying profits to his cousin George's family who still owned half the company. During this time, he also began moving assets between divisions and shell companies in an effort to gain more control and a greater share of ownership. It is also during this time that he brought his son Arthur Telemachus into the business, and grew the company considerably.
In the early to mid 1990's, George's heirs (including Arthur S) sued, claiming that they were defrauded by Telemachus and Arthur T, and were left with only 8% of the company. A court found in their favor, and awarded them additional shares of the company to bring their total ownership to 50.5%. Despite this, Arthur T was elected to CEO in 2008.
In 2013, the board unsuccessfully attempted to remove Arthur T. He was then fired in 2014 during what looked like an attempt by the majority shareholders to squeeze money out of the company and then sell.
98 years of family politics, fraud, and freeloading- It's easy to see where tempers could get involved.
My take is this:
Artie T and his father illegally tried to gain ownership of the company that they were successfully running, away from the half of the family that were sitting back and letting them do all the work.
I think they were justified in keeping the lion's share for themselves, but went about doing so in an unethical and illegal way, and it bit them in the ass.
Again, I see it as a macrocosm of the kind of capitalism that makes money by working hard and building things, versus the kind of capitalism that makes money by owning things and taking credit for other people working hard. I am unapologetic in my biases.