OK, I just a quick look at your profile, and the stocking stated in that.
WIth a 64l tank, 2 shoals of tetras and half a shoal of peppered cories, there isn't a huge amount of fish that you could have in addition to.
My favoured advice would be to increase the cories to 6, and you could then just about accommodate 3 male endlers.
Option 2 would be 3 male guppies but no extra cories.