Peacock cichlids are African cichlids (your severums are S. American) so should not really be mixed, besides which your tank is way too small for the severums let alone a peacock cichlid which could get 6" or possibly more. If you really really have to add some tank mates get a small group of bleeding heart or serpae tetra. A 20G is nowhere near big enough for one severum let alone 2.