Could someone explain the boxing style of each Black Murderers Row member?

That is a huge ask.

Holman Williams was probably the best of them after Charley Burley, his style was shining, he had bad hands and although something of a puncher as a youngster, he had to sheathe most of his hardest punches with his schedule. He really, really fought at a significant disadvantage. He looked for volume, he would happily give ground rather than fight that war unless the stakes were especially high but he could bring pressure when required as he did in the final third of his 1939 points win over Burley. It's very very hard to find modern comparisons but think of a 130lb Floyd Mayweather, perhaps.