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In short - yes, you can assign multiple people to the administrators group. Careful communication between admins is imperative.
Based on my experience, I think it best to create a new admins group with all the same privileges of the default admins group. Some modules give the default admins permissions to everything, which is understandable, but it can lead to disclosing information not intended to disclose.
Example - not that this really exists in a XOOPS system, but: You are the admin of a site for a bank (lawyer, doctor, whatever) that has confidentiality rules. As admin, you have access by default to all information. Just something to be aware of.