Adding more clowns

[hummer]

Hi,
I have two (orange/white) tank bred percula clowns in my 80 gallon tank and was wondering if there is a big risk adding two more tank bred percula clowns? My current clowns are about 2 1/2 - 3 inches. The ones I want to add in are smaller. Maybe 1 1/2 - 2 inches. I heard mixing clowns are bad but I've added Black/White percula clowns before and they got along just fine. I lost them, and a few others, to a slight disaster though.

Other tank inhabitants:
Blue Tang ( about 4-5 inches )
Yellow Goby
Spotted Cardinalfish
6 line wrasse

Thanks for any help.