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...

Hens go broody when you don’t want them to… and won’t go broody when you do.
I love Seramas 
only 1 Serema though
I wanted 3, min. Turns out 2 were Cochin eggs >,<
