Why do all characters equip the same weapon in Duet Night Abyss?

Hey everyone, I just started playing Duet Night Abyss(not experienced in warframe) and I’m a bit confused about the weapon system.

When I equip one character with a weapon, it seems like *everyone* gets equipped with the same weapon.

Is this supposed to happen or am I missing something in the settings?

Also, does the same thing apply to demon wedges?

Thanks in advance!