With those pics it's a bit hard to tell. If you got a pic of the underside of both then it would be easier. The green one appears to be female based on last segment being so large. The other one I can't tell.i agree!
In alot of mantids the size difference isn't really obvious as nymphs. Some more experienced people can see a difference but it's not a reliable way to tell.Yeah, I think the green one is female. I'm not too sure about the brown one but I think it's female too. I expect males to be skinnier.