Haven't heard the one crest feathers one before, worth checking it out. Truth is many have their way of sexing. Amount of barring on the backs is a very common one and works on chicks slightly older than your pair, because they need to go thru more feather growth before less vs more barring becomes evident. I start guessing as soon as the peachicks get their neck feathers. The females show an early version of the 'lacing' on young and adult peahens- dark feathers edged in buff color. I could see some of those on the right chick... On boys the neck feathers are more variably patterned showing some little dots plus on many the light colored area below the neck is whiter than on girls. (edited to add, I look at front of the necks not on backs for the patterning and the dots on boys are dark, not light little dots- it's in the same general area in below comment regarding zazouse pics)
In zazouse's pictures, you can already well developed dark feathers with buff lacing on the girls and the boy has an clearly whiter area below the neck- also look at the border between the white area and colored neck, some individual feathers have a spot or two spots on each feather. This can show up really early, before the amount of barring is very clear.
Others swear by sexing the primaries right at hatch, boys have reddish, girls have brown.. have not been able to see the difference on this myself until the birds are older and already showing differences in neck and barring though