There are a lot of strange EC meetings (sorry couldn’t help myself).
Re some of the legalities – Jimmy is right, if someone sells then they can’t be on the EC so there is no need for a resignation letter, refer section . That element doesn’t matter.
In relation to the other two, the Act provides that the position is vacated upon receipt of written notice. However, from what you have said out of the five members there were possibly only one or two of the existing EC members there? – so as Jimmy says the meeting didn’t have a quorum so technically there was no meeting.
Note that the usual procedure when someone resigns (setting aside the two who had sold) is that they resign effective as at the end of the meeting, that way the meeting has a quorum and can effect any business it needs to get done.
I’m not sure why the manager said you only needed to elect three members if four had resigned.
In relation to electing EC members – strictly speaking Schedule 3 provides that where a vacancy occurs the owners corporation must elect someone to fill that vacancy – para 4(4) of Schedule 3. I know this has been debated before and some people won’t agree with me, but I believe that means the owners corporation in a general meeting. Whatever – it is a completely unworkable provision.
I suggest the easiest solution is this. Scrap that meeting, it didn’t have a quorum. Call another meeting and make sure the three existing EC members (including you) are there so you have a quorum. Get the two resigning members to do letters resigning at the end of that meeting, and then proceed with the meeting.
You will just have to elect new EC members at that meeting, because otherwise you can’t do anything once the two other members have gone. Unless you want to have a general meeting, and you can elect the members then!