eep, yes, definatly keep him away from the others! Rats contract sicknesses very easily..Does he have any porphryin (red discharge around his nose??) So sorry to hear he's sick..
I've never given my rats that type of medicine before, so I don't know anything about it..

It's very possible that the could be from the same litter. All different patterns and colours can come from the same litter. Icarus is an agouti hooded, and in his litter he had another agouti hooded, an agouti veriegated, a black verigated, and a fawn hooded.