Yes there are alot of people that either by ignorance or intention do the knock-off thing...
Olive/green legs are still a serama trait, so that is no problem...
GENERALLY speaking when the serama has been intermixed with OEGBs [ which is the most common mixing] what pops up is long backs, WHITE legs, different shaped combs, more horizontal wing carriage and a tail that isn't "perky" and vertical like a serama...so those are dead giveaways to intermixing breeds.....
Just curious, do these 4 gremlins share the same parents? LOL
I am not sure, but I can ask the woman I am getting them from. I'm up in Canada, and basically nobody has anything rare, so I take what I can get. It seems to me like the cockerel has already got almost proper posture...