I would not reccomend sexing buttons solely based on the sounds they make. Yes, male and females do have different sounds but they also have a lot of similar sounds, especially young birds. It's easier and more accurate to visually sex them since males and females have very different plumages in every color except for pure whites and some tuxedos.
When i'm sexing buttons i usually look for:
1. Visual: Does the bird have any blue chest feathers, red vent feathers or the typical "bib" underneath the chin. (All 3 are signs of a male)
2. Behavior: Does the bird offer treats to the others. (Males offer treats to females)
3. Sound: if i'm still a bit unsure after i've looked at the other signs then i'll look at the sounds they make but most buttons can be sexed by only using the first step.
I said that the two white ones were females mostly based on their color, the sound they made just made me 100% sure. If you had only posted the sound with no pic of the bird then i wouldn't have been able to tell.
This was a very long reply but i hope it helps!
