The Estate is the owner of the three units, although perhaps that has to be confirmed via probate.
Why don’t you delay the AGM until after probate? A call to Fair Trading would sort out whether that’s a reasonable thing to do. In fact, my strata plan just delayed the AGM because someone was on holidays so I’m sure it happens all the time without someone from Fair Trading arriving with a wrecking ball to demolish the building because your AGM wasn’t held on time.
Just make sure the other owner is ok with it, and make your lives easy. Delay and if any urgent issues arise, such as an insurance renewal, deal with those via email.