Veronica's husband, Harry, was planning to double cross both the Mannings and the Mulligans. He was pulling a job to steal $2M for the Mannings, because Jamal Manning needed most of that money for his campaign. Behind Jamal's back, Harry made a side deal with Jack Mulligan in which Harry faked his death and keep the money while splitting it with Jack and therefore cripple Jamal's campaign. This was why Jamal was so desperate to get that money and forced Veronica's hand. Unbeknownst to Jack Mulligan, Harry had his own plans to rob him of not just his half, but the full $5M he got stashed from embezzlement of his own donations. He knew that the Mulligans wouldn't dare claim they were robbed because that'll open a whole new can of worms as to where they got that money from being that it was stolen money to begin with. So, the plan was initially for O'Reilly, their driver, to sell off the book to the Mannings and that'll so call pay their debt and he was planning to rob them after the heist was done, but Veronica intercepted it and decided to fulfill it out on her own. Regardless, Jamal wasn't with selling off the book when his brother, made mention of it, he wanted the cash on hand. So Jamal's brother decided to go on his own to scoop out what Veronica is doing with the intent of robbing her and he roll out with the cash. The only reason he didn't kill them was his own underestimation to which was part of the theme throughout about the assumption that they're women and wouldn't dare pose a threat. This had nothing to do with the elder Mulligan. It was incidental of him showing up. Like Harry told Veronica when he finally appeared, the job was supposed to been easy. So, murder wasn't part of the equation. Harry didn't care or was favoring one side or another, all he cared about was his new family with his mistress and them getting the cash and dip. His plan was to fukk everybody over all at once.