Well, i'm sure you already know this but make sure everybody is getting enough food and space it keeps the competition factor down. Also its a good idea to get another angel if there is enough space. I have two smaller angels in my tank with a puffer and gourami, I find the angels stick together and keep my puffer in line when he decides to be bad. ;D But all in all everybody gets along well.
JiMZz Welcome to FishLore if you haven't already done so please step into the welcome forum and let us welcome you properly
Now I really hate to tell you but your tank a little crowded. Angels and GouramI both are very territorial and there's just not room for all of them to find a space of their own, that's why the one you just added is getting beat up. I would definitely not add anymore fish and would even take the last angel back.
The Gouramis and the angel have still set up territories and will not accept another angel as you have seen. To throw another angel into the mix is just asking for more displays of aggression. Sorry.