Yeah, the client needs to support zap splits, but essentially you fetch invoices from each users, lighting address, and pay all the invoices. Currently snort, amethyst, and http://zapper.nostrapps.org support paying zap splits.
and if I zap a note with multiple zap tags on a client that doesn’t support it, like damus, I assume im only zapping the note poster? eg if I zap nostr:note1zv7lsh08pymmu4ks0k79fjzhfwzd2ug7cmh0ju0mfzwzdvpkrr9q6mc6wq I am only zapping you.