Cichlid Is Being A Bully But Why Now?

I have a Cichlid tank with 2 male bumble bees and cobalt and blue zebra. I am not 100% sure but I am pretty sure all my blues are females and my 2 bumble bees are no doubt males. I've had them for over a year now and they've been perfectly fine. Recently the dominant male, Mushu, has been over aggressive with his brother and pretty much wants him gone. The time this aggression started was about 2 weeks ago, the same time Mushu started making a "nest", or what I think is a nest. Normally Mushu loves the front of the tank but he's been clearing out this cave and spitting rocks all over, he dug to the bottom of the tank. I know it's normal for cichlids to move rocks but normally they only do it when looking for food are when I vacuum the rocks they will clean up whatever rocks ended up on the decor. Mushu has taken it to a whole new level, which is fine, it's their home, not mine, they can move whatever they want but I feel it's linked to his aggression issues that started up.
The first thing that came to my mind is that he wants a mate and wants the other male out of the way. The only problem is he's displaying his darker colors instead of the brighter colors and I've seen 0 effort on his part to woo the ladies. Does anyone have any ideas? I don't want him to kill Scar. I recently added some Hornwort but the fish don't give 2 fins about it. I know from past experiences with cichlids that if the cause isn't found and the fish being bullied doesn't end up removed from the situation it will end up dead. I wanna try to fix it if I can cuz I like Scar and I really don't wanna have to rehome him or Mushu.

 

Mushu is ready to mate and is becoming violent as a result. Possibly the addition of two or more females could help with this, but you most likely will have to separate Mushu

 

Mushu is ready to mate and is becoming violent as a result. Possibly the addition of two or more females could help with this, but you most likely will have to separate Mushu

So Mushu wants to kill Scar then become friendly with the ladies? There's a lot of ladies for him to choose from. That kind of sucks. I guess if I have to rehome him I can but dang those 2 bumble bees looked great surrounded by all the blue.

 

Or you can attempt to add a new addition to throw a wrench in the territorial establishment, which can give them an opportunity to establish their sides of the tank

Talking about decor

 

Whats the tank size? Is it just the four fish?

 

How large is the tank? Bumblebees get large for mbuna and often times even a 55gal isn’t good enough.

In all you have 4 cichlids right? African cichlids really need to be over stocked to spread aggression and keep the dominant fish from picking on just one.

Your bumblebees have probably just reached sexual maturity and are looking for love.

 

Whats the tank size? Is it just the four fish?

4? No no no, I got the 2 bumble bees, 4 Zebras and 3 Cobalts housed in a 55g. Mushu is the biggest boy. I can't tell too well how big he is in the tank but I'd say from his mouth to the tip of his tail he might be about 4 inches. I might have to take him out the next time I clean and measure him to make sure. Scar is leaner than him and not as long. My smallest fish is roughly 2 inches. All the females are a lot smaller than Mushu but not too small. I've seen a lot of mixed answers on the internet about the actually max size for bumblebees and from what I can gather 6"-7" seems to be the safest answer. So he's no means full size yet.
I do have plans later in the future for a bigger cichlid tank just because I love this fish so much and I mean... really... who in this hobby don't like hoarding fish when possible. I wanted to stock more Cichlids in this tank but I really don't know if I should, The tank is a corner tank, and since they aren't full size yet I don't want them outgrowing the tank before I can get a larger tank, if you know what I mean. The fish have plenty of room for swimming right now and haven't outgrown it. Lot's of hiding places. I really so badly want to plant the heck out of the tank but there's a CO2 problem with keeping the current plants alive so until I buy a CO2 reactor or end up making one I can't grow any nice looking plants. Not to mention the cichlids like to peck at them and bury them under rocks.