A quick but meaningful question

Where is a "group marriage" legal and hopefully respected?
To explain what I mean as I am pretty sure "group marriage" is the appropriate term but just in case... I(M2F) have gone from nothing to two others both male. I wish to fine a legal arrangement that ensures legal rights between us. I explicitly wish to ensure my partners have a legal say should anything happen to me. Especially medical things.
Would anyone have any ideas, suggestions or the like?
Thank you.
*curtsy**edit* For any whom care or might be interested,
unmarried.org would seem to have useful data, in particular their /legal-financial-f.a.q.html