.. that an untapped vampire playing Familial Bond is tapped before the end of the action, the combat bound happen because Familial Bond will not take place?
Imagine the following situation: A vampire, with superior Obfuscate, let's say Evan Klein (with a Blithe Acceptance) is attempting to bleed. On the other hand a Laibon vampire, let's say Amavi, is trying to block the action, using the +1 intercept to match the +1 stealth of the bleed action. Then Evan Klein uses Faceless Night (at superior) to give the action an additional stealth. Amavi fails to block, and Evan Klein decides to let the action be successful (he needs to make that decision at this point because of Familial Bond). Evan Klein then bleeds successfully, but no combat occurs with Amavi after the resolution of the bleed.
But why is there no combat? There are two things which makes this transparent: At first it is the sequencing within the action. During resolution of the action the second effect of Faceless Night is applied, i.e. tapping the minions who attempted to block. After resolution of the action, the combat due to the effect of Familial Bond would occur. And here the second thing for understanding is that the cards require the reacting Laibon needs to tap in order to enter combat with the acting minion. But since he's already tapped by Faceless Night, he doesn't fulfill the necessary requirement for initiating the combat.