I don’t know if they are strictly legal and I suspect that they aren’t (and if they aren’t, then the by-law has no standing since you can’t create a by-law that infringes another law).
However, if you were to word the by-law that allowed the concierge to, say, cut off the electricity supply if there was a concern about fire safety in any unit to which they couldn’t gain access, that might be different matter. My legal friends may advise on this but as it stands you could be on shaky ground, legally.
But seriously, it sounds like this pig of an owner and his spoilt brat son need a reality check. I assume you have already:
a) Approved a motion at an EC meeting to issue a Notice To Comply. (If not, you'll find the official NTC form here)
b) taken this to Fair Trading for meditation – a prerequisite for CTTT action (Form).
c) Pursued this through the CTTT for enforcement of your Notices to Comply.
If you have tried all these and they have failed, your next step should be to gather evidence and go to your District Court and ask for a noise abatement order to be imposed on both the son and the father (as the ‘tenant’ and the owner).
If that succeeds, any further breaches would be a criminal offence as they would technically be a contempt of court and the offenders could be arrested. Have a look at this link on how to get a noise abatement order, and take it from there.
In the real world, there are plenty of things that go on that aren’t strictly legal (but bloody effective). For instance, if the other owners had an audit of electronic keys and one owner was mysteriously left out (because the notices were slid under his door rather than posted, for example) and he later found out he couldn’t access the building and concierges were under strict instructions not to allow access to anyone who couldn’t prove residency … well that would be a terrible thing.
But seriously, go back to the law, gather overwhelming evidence that the idiot father and the brat son are flaunting any reasonable standards of decent behaviour and take them all the way (and don’t forget to collect costs and damages if you can get them – you won't at the CTTT but you could at proper courts).
I can think of half a dozen strata lawyers who would love to take this case on. And with a reasonable chance of getting a result and costs – why not go for it?
By the way, this is a process that you have to begin now regardless of when the most recent breach occurred. Party season is just starting so I would get on to it right away.