One pilot making an error OK, but 2 pilots making the same error at the same time?
I don't think that 2 people made the same error at all. I think that one person looked at the NOTAMs (maybe) and one person listened to the ATIS. The second person's error was in not getting the ATIS themselves. There's no point to working out the data separately (did they do that, I wonder), if you haven't sourced it yourself.
Maybe coughpit culture but also calls into question the upline corporate governance.
Yes. QF isn't perfect, but we were pretty fanatical about each pilot individually gathering the data for the take off calculations, with no crossover until you had an answer. And extra pilots were expected to take part too.
Q: When do airlines run a 3 pilot mission? 8hrs duration or more?
Varies with the nationality of the airline.
Q: Sloppiness can often be picked up in sims, but there is only so much sim time to go around.
Sims don't pick up this sort of error. Annual route checks, and standards checks are meant to, but people who skip steps often put them back if they know they're being looked at.
Its not my spelling :

pit correctly spelled appears as coughpit for some reason
Seems appropriate.
Pilots are not necessarily 100% at fault here, considerable concern needs to be put on the flight dispatchers who provided a report that the airport had no significant applicable notams
Yes, but you aren't supposed to take that as gospel, and then check no further. It means that they didn't notice anything. Beyond that though, I doubt that either of these mobs have an actual planner in Melbourne. The data would have come from overseas to their iPads.
while in the case of MH the MAB briefing and OFB had inadequate space for the complete ATIS.
That's only a bit of paper. If you get the ATIS on the ACARs it prints out as much as there is. In any case, there's plenty of blank space available.
Not only did they miss the NOTAM's, the ATIS message that was current at the time mentioned the shortened runway before it went on to mention the conditions - so the pilots basically tuned out on the information about the shortened runway and basically were going "come on, come on - get to the conditions stuff that we need".
My take is pilot, not pilots.
The fact that pilots from two different airlines both missed (ignored) multiple opportunities to receive the information is a worrying sign for the future of aviation...
Don't check, she'll be right.
AS I mentioned upthread the OFB didn’t have room for the non normal ATIS stuff in both cases.
Write smaller.