Whose tax and bank information should go into a CreateSpace 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, and I set up a separate CS account for him under his name but with my company's tax information (this was before CreateSpace discouraged multiple accounts for the same person.) In the future, I'll probably just publish all books under my own main account if I'm paying out royalties (except for this one customer, obviously.)
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.
You may also want to review this FAQ question as well: Should I set up a client’s accounts or have them do it?