Italy still doesn't allow same sex marriages therefore the language hasn't evolved a way to address these cases, yet. However I'd say: sono sposate or (horrible horrible form): sono moglie e moglie.
To answer your question, sono mogli doesn't mean that they are married to each other.
Is this still the case in Italy? Even if Italy doesn't allow it plenty of other countries do. Presumably two internationally inclined Italians speaking Italian may need a way to articulate a same sex marriage? These little quirks always surprise me :)
EDIT: For those that are interested, same-sex marriage is an open debate in Italy, but it still remains the only country in the western world to not explicitly allow same sex partnerships. Change is a foot, but still this really surprised me!
Italy has recently introduced a partnership (Unione Civile, reserved to same-sex couples) that is sorta kinda similar to a marriage (which is still reserved to man-woman couples).
From what I've read, there are some differences (in brackets the rules for married couples):
- divorce can be granted three months after the request (vs 6 to 12 months)
- partners can keep their last name (vs the wife must take the husband's name)
- adoption of the partner's children is subjected to a court decision, ie not granted by the Unione Civile (vs almost automatic)
- no expectations of faithfulness (vs expectations of faithfulness)