4-5 month old mbuna fry starting to get rough!

So it is time to do something with my 4 month old OB red zebras (~15) & my 5 month old albino socolofi (~20) because they are starting to fight, just as of a few days ago really! I found one dead this morning with a red mark on it's side (see picture) and I think it may be due to fighting. A lot of them are breathing heavy now too. I know I need to do something now but can't decide on what to do.

The main purpose of growing them out was to get a couple more females (and maybe some with some blotches with the OBs) but I don't think I will be able to house them ALL to a sexable size if they are already this aggressive. BUT I was able to keep 40+ up to 3+ inches in my main tank until I was able to sex them BUT they were 6 different species this is only 2, I would think that would cause an increase in aggression.

If I wanted to keep these guys until sexable what is the minimum tank(s) size I'd need? Separate tanks? and what would be the absolute smallest size they'd have to be to be sexed fairly accurately? BTW they are all around 1.75' right now.

Thanks guys! I have been trying to figure out a solution. The problem is space for a bigger tank, I just don't have it. I could try swapping some stuff and setup my 58g but it is still only 3ft and needs parts. I COULD convert my 33g(3ft) to a rocky tank and split them between that and my other 30g(3ft). That would sustain them for a little while at least right? At least for the next few weeks until I know whether I will continue to have a job or not!

I do 50% WC weekly & twice a day feeding and think they have done quite well. Why the 4mo & 3mo are the same size I am not sure though, especially considering the 3mo OBs were noticeably smaller then the albinos as they developed (comparing them at the same ages). I have noticed incredible growth spurts when they change tanks though. Even the fish in the main tank, they grew like crazy at first and now they don't seem to grow at all even though 98% of them are no where near adult sizes.

I did add an Emperor 400 and they are doing much better! I added more rocks too and the fighting has pretty much stopped! I am happy with the short terms fixes but I know something has to be done for the long term.

Most crucial question still remains, What is the smallest size I could vent them and get reasonably accurate results? I am thinking maybe 2.5"?

Excellent! I only really need 2-4 females out of these 35 so if at 2.25" I can cut it down to 10 possible females I'd only need to be 40% accurate to get what I want. I really think I could even just sell half of them now and still be safe but the odds have not been kind to me in the past so I don't think I wanna risk it. Thank you efors!!