When stocking a tank you shouldnt always think hmm i wonder what i can get away with in there, when you buy them if theres any doubt then your are probably over stocked,
Im not saying you are btw
And i would rather 2 or 3 nice fish in one tank with plenty of swimming space etc with less maintainence than a tank crammed full of unhappy fish, while your constantly cleanin up there toilet tere swimming around in
Your mates fish may not have diseases etc but i can bet they wont live anywhere near there ful ife expectancy