I don't know how the "frivolity" rules in Connecticut work, but even if you hold mortgage AND the title (or a deed to secure debt), you cannot just walk in and change the locks on a tenant in possession. At a bare minimum, the bishop should have filed a dispossessory, and the parish was certainly entitled to a hearing. Contesting that is NOT frivolous by any stretch of the imagination.
In fact, I think a claim for wrongful eviction would be in order. I can't imagine that a liberal state like Connecticut doesn't have landlord-tenant laws slanted in favor of the tenant.
All true, IF the vestrymen are a "tenant in possession".
Legally, though, the tenant may very well be the bishop and the diocese, and the congregation could be invitees, who can be excluded.
I have to expect that Episcopalians in Connecticut can get good legal counsel. So, if they haven't filed a TRO yet, I'd expect there's a reason. Maybe it's lacakdaisical lawyering, but I suspect it's that the case is not strong.