Whose tax and bank information should go into a KDP Print account?
For my clients, I usually do my work for a flat fee, so if I’m setting up their account then I will either enter their banking information for them or have them enter it once the account is created.
For the client that I am paying royalties, then I have his Kindle books under my own account.
My suggestion is that if you are working on a royalty arrangement, have a contract in place dictating who collects the royalties, how much they are for, and when payments will be made. I suggest that you (as the publisher) collect all of the payments and then distribute the royalties on whatever schedule is agreed on. Keep in mind that you don’t get the payments from Amazon right away, potentially 60 days after a paperback sale and 90 days for a Kindle sale.