Nice . As I recall the only way to stop / avoid bullying and even terrorising is to overcrowd the tank with loads if Malawis tbh.
Loads of rocks and hides helps somewhat or delays the inevitable but adding as many fish as you can afford is the way forward.
A good filtration system and regular water changes as well , I had 3 internal filters working in mine but a decent outside filter also works wonders.
I'd add as many Yellow Labs as you can afford. They are about $4 each around our way . 6 for $20
https://i1.ytimg.com/vi/V953Pv95n-Q/hqdefault.jpg