Who are the five families in London?

[Trading Spaces]

The biggest prop firms, known as “the five families,” were based in London and had dozens of traders on their books, many of whom had come from the pits.

For a long time, Commins and much of his crew traded as an off-site offshoot of Tower Trading Group, one of the five families.

I am guessing GHF who are mentioned in the article. Who else?

Negative Oil: When Prices Went Below Zero, These Essex Traders Made Millions - Bloomberg