Why is "They are wearing their shirts" not an acceptable answer?
How would you say "They [i.e. a group of people] are wearing their [i.e. a different group's] shirts"? I know it's a weird sentence, but I'm mainly interested in how one distinguishes between "their own" and "other people's". I understand with one person you say: "Han har på seg skjorte" = He is wearing his shirt. "Han har på hans skjorte" = He is wearing a different boy's shirt.
It isn't the correct translation, because the Norwegian doesn't specify whose shirts they are. If you want to add this extra information, you need to add a possessive pronoun (my/mine, you/yours, her/hers). e.g.
De har på seg skjorter mine = they are wearing my shirts. De har på seg skjorter hennes = they are wearing her shirts. De har på seg skjorter deres = they are wearing their shirts
So there is a ø in skirt, but not in shirt.
I hope that after writing this comment I will remember them myself. I kinda always mix them up.