"Since the plaintiffs never appealed the bankruptcy court's confirmation order, the order is a final judgment and plaintiffs cannot challenge the bankruptcy court's jurisdiction over the subject matter.) (citations omitted); Lawrence Tractor Co. v. Gregory (In re Gregory), 705 F.2d 1118, 1121 (9th Cir. 1983) (declining to consider the legality of a confirmed Chapter 13 plan because [t]he order c" . . . .