I am new to quail but have looked up different ways on sexing.
3 & 6 look like boys based on the brownish feathering on the chest. 4 is questionable as it does not have as a pronounced brown color on the chest feathers.
I'm not sure how early males will do this, I'm thinking @ at least 6wks of age - if you turn the quail upside down & pull it's tail feathers towards it's back -if it's a he - he will release a white foam.
Hope to have been some help!