Ah, okay, well first I either misused or found a bug in the unspent ["address",...] command. It didn't work when I put brackets around a single address, but only with no brackets.

Second, the way this will work, nobody will ever have all the keys to redeem the transaction, they will be signed independently and only the signed transactions will be shared. So listunspent seems not to work in that case.

Is there any way I can glean this info from a bitcoind client? Or do I have to use something like the blockchain.info api to find unspent transactions for arbitrary multisig addresses?