The Lions clinched at least the # 3 seed in the NFC, as a result of the win over the Vikings this past Sunday.
If the Lions win the two remaining games, the Lions clinch at least the # 2 seed, as the Lions would have the tiebreaker over the Eagles at 13-4.
It would be shocking if Washington beat the SF 49ers this coming Sunday. While the 49ers will be favorite against the LA Rams, barring possibly multiple key injuries, the Rams have been playing as well as any team in the NFC over the last few combined games. If the Lions upset the Cowboys on the road and beat the Vikings at home, there's at least a realistic chance the Lions are the # 1 seed.
If the Cowboys beat the Lions, it's highly likely the Lions will be the # 3 seed.