Family was once, at least in theory, the reason for Walt's actions. Breaking Bad's pilot opened with Walt desperately addressing his family: "I just want you to know that, no matter how it may look, I only had you in my heart." Since then, whenever Walt has needed justification for his extreme actions, he's turned to "family," and most recently, it was Gus Fring's terrible threat—"I will kill your wife. I will kill your son. I will kill your infant daughter."—that set Walt on his path to triumph.
One of the most disturbing aspects of the Breaking Bad universe is the idea that caring about people is just a weakness to be exploited. If Jesse hadn't cared so much about his girlfriend's son Brock—a pair that represented a new family for a man who had been ousted by his own parents—Walt could never have turned him against Gus Fring, who represented the latest in a long string of adopted father figures for Jesse. One of Walt's subtler cruelties was taking Jesse's need to protect his newly adopted family—feelings that Walt, more than anyone else, should understand—and using it against him.
But even the series' most powerful characters have been brought down by their attachments to their loved ones. Let's not forget that family was Gus' motivation—and ultimate downfall—as well. The murder of Max, the other "hermano" from Los Pollos Hermanos, was the reason Gus went out of his way to torment Tio Salamanca (who got the last laugh when he set off Walt's wheelchair bomb). It's hard to imagine, despite what he says, that Walt's family occupies a large place in whatever heart he has left, which makes him Breaking Bad's least vulnerable character.
But the moral heart of "Madrigal" centered on families we met for the first time: Mike's granddaughter and Lydia's daughter, two young innocents who have unknowingly been drawn into Walter White's increasingly-complex web. Mike unknowingly sealed his own fate in last week's episode when he helped Walt and Jesse destroy Gus' laptop, which led the DEA to discover the offshore bank account that contained more than $2 million for his granddaughter Kaylee. (It's a testament to the strength of Breaking Bad's writingthat our sympathies are against the two DEA agents trying to bring down a meth ring, and for a selfishly-motivated killer.) Mike, like Walt, is suddenly in the hole—and like Walt, he opts out of attempting to climb out in favor of attempting to find an exit by digging in deeper.
But Mike also has a second "family" that lets him down by the episode's end: the carefully chosen team of allies whom he hand-selected to work alongside him. "My guys are solid," says Mike, with an almost paternal defensiveness, as he refuses Lydia's offer to take the men out, trusting that they'll stonewall the DEA just as thoroughly he did. But he's wrong. It's less than a day before Mike's former ally Chris betrays him (though Mike, always one step ahead, manages to catch him in time to take him out). There's a biblical overtone to "Madrigal," which sees Mike betrayed by the Judas of his 12 disciples, though Chris' apology isn't enough to stop Mike from responding to the betrayal with a bullet.