Well It is strain dependent you said you have 3 doubleberry and one og kush would it be the kush that is not showing? they've been in a monthish? what do you mean in? In veg or flower? If they have been in flower for a month or atleast the flower time schedule they really should all be showing sex by now.
*Edit* Ahh nevermind I reread your post they are obviously in flower. it may still be the strain but a month sounds a little long to show sex.