Or, I suppose, they could ALL be Mjolnir, just not the version that we know.
Maybe the god of Fear is bringing forth different Mjolnirs from past Ragnaroks? That would explain it.
So... who of those 3 would be worthy? I'd say none of them, but maybe the standards for worthiness is different depending on which incarnation of Thor has wielded each Mjolnir?
I do like the idea of all the hammers being a version of Mjolnir. That in itself could be a very fun and interesting story. I was a little iffy on this upcoming event as I buy comics on a budget as a single dad and only have Thor, the Loki and Thunderstrike minis on my pull right now.