The first three interpretations are correct.
There's a missing preposition in your examples that makes a difference to the interpretation of the fourth example.
As you have mentioned, the past perfect is used to convey that something happened before some other action in the past. In your fourth example the bust-up is the action that occurred before something else, but it's not clear what that something else is. Depending on the preposition it could be several things.
'During lunchtime' - lunchtime is an extended time period and the bust-up occurred before some point within that period, but it might have started during that period, too. Most people would understand that it started and finished while lunch was going on, so you can't use past perfect here.
If it started before lunch and ended during lunch you would have to be more clear.
Yesterday at lunch we had a bust-up. It had started before the meal but didn't finish until we were done eating.
'At lunchtime' - this could mean the same thing as 'during' or it could mean 'at the beginning of'. You can use past perfect for the second case because the bust-up is finished before the beginning of lunch, but not the first case. Because it's ambiguous this is not a good preposition to use.
'By lunchtime' - this is the only case where it's absolutely clear that the bust-up was finished at lunchtime and you can use past perfect.
Yesterday by lunchtime we had had a bust-up.
The lesson here is that shades of meaning make a difference and even native speakers understand this in different ways, so be very clear with what you mean.