ISA users are not able to manage Collections. An ISA user can add a System or an Account TO a Collection, as long as they have ISA permission on both the Collection and the System or Account in question, but they can't manage the Collection object directly.
An ISA user does not have the ability to manage TPAM Users. The "Users & Groups" menu is hidden from them.
A User Admin can delete Basic users, but not Administrators.