Presumably, choir will have ashes imposed at 7:25PM, before liturgy begins.
Juxta: women on psalm tone.
Emendemus: men. Cantors alone on verses (“Adjuva nos…” and “Gloria Patri…”). All at repeats of “Attende Domine…”
Kyrie: men and women could alternate, if you know it well enough.
Gradual: women on psalm tone.