I misunderstood the question, so I'll take a re-do please
The longest I have gone without feeding adults is 2 weeks. No negative side affects. Depending on how large the juvies are you can go a pretty long time. Your tropheus would be fine for 2 weeks.
The most I am comfortable with is 10 days to be gone. After that point I start freakn out and not enjoying my vacation. So... we try to limit our vacations to 10 days
IF I only had 2 tanks with the fish you mentioned. I'd leave for 2 weeks all the time... I might even do a bit more than that.
I very rarely have a sitter come in... I just leave and go have fun and the fish are fine. Very rarely do I come back to dead fish.. unless they are fry. ( thats why you see me put up fry at stupid prices ... I feel bad and don't want to kill them). I have had 2 sitters come in over all these years. 1 was a disaster... the second was Donna. DOnna did a great job. Fish spawned while I has gone and I came back to happy healthy fish. SHe knew I was going to be gone for 10 days... so she fed lightly and didn't turn the water into nitrate muck !