Question about Executive Officers..

I am losing track of the Executive Officers.

1. Is Xaden's Executive Officer of Fourth Wing ever named? What happens to them?

2. Sienna is named as Dain's EO of Second Squad / Flame Section but then what happens to her?

3. Does Dain have an EO of Fourth Wing when he becomes Wing Leader? Who is it?

4. Bodhi is switched to Flame Section Leader after Varnish's dragon takes out most of Third Wing .... does he have an EO?

It seems like an important position and either they are not mentioned by name a lot or I am just losing track of them ... Is one of the Section Leaders the WingLeaders EO .... like is Garrick, Section Leader of Flame Section and also Xaden's EO. Help? Thank you