Common games is the tiebreaker BEFORE conference tie breaker. Doesn't change your analysis but just wanted to point out the order of tiebreakers:
It's head to head, then division, then common games, then conference record.
We need Philly to lose one more game. If they lose to the Giants, as long as we finish with same record, we'd win the division based on divisional record (Washington not pulling one of those two games against Philly hurts). If they lose to the Seahawks or Cards, we can actually lose on more game ourselves but is has to be Detroit. That's the only game (other than Washington) that we could lose and still get the division in a tiebreaker situation. If we lose to Buffalo or Miami, we are done in terms of tiebreakers (which makes the Cards loss all that more appalling) unless the unthinkable happens, and they lose to the Giants.