Angel fish advice needed

[wookie]

Hi,

I currently have a fairly aggressive pair of angels in a tank with a school of Tetras and a medium sized gourami. They are getting on ok at the moment but I would like to add another 4 smaller sized angels into the tank. Has anyone got any advice on the best way to do this without the original angels causing problems?

Thanks.

[Hypostomus]

...what size tank is it?