If I had a non-HD multi-sig wallet, checking the balance of it would be trivial (I would just look at the blockchain to see the address' balance, without the need to hold a key).
However, with HD wallets, a wallet is comprised of N addresses. So knowing the balance of this wallet is not easy unless you are one of the key holders.
Therefore, this is my question: how to know the balance of a multi-sig HD wallet, from a read-only standpoint? Can the distribution of the keys be asymmetric so that there's one key that allows checking the balance but doesn't allow signing?