User blog comment:Paul.rea/Teen Wolf News 112313/@comment-5455946-20131123162859/@comment-4091815-20131123191156

Peter is a "self declared" alpha.

He's exhibited no Alpha like behavior, his eyes are blue, and he stated in Season 2 that he was weaker and needed to be part of a pack with an Alpha like Derek.

There is no indication at all that his Alpha status survived his death - Derek took it from him when he killed him.

With the twins, it seems, since they killed an Alpha while they were merged - the merged being became an Alpha.

If they are no longer able to merge, if the merged being is "dead," then they no longer have access to the Alpha level power.