§7.3.3/3:
In a using-declaration used as a member-declaration, the nested-name-specifier shall name a base class of the class being defined. If such a using-declaration names a constructor, the nested-name-specifier shall name a direct base class of the class being defined; otherwise it introduces the set of declarations found by member name lookup (10.2, 3.4.3.1).
¶14:
… [ Note: Two using-declarations may introduce functions with the same name and the same parameter types. If, for a call to an unqualified function name, function overload resolution selects the functions introduced by such using-declarations, the function call is ill-formed.
¶16:
For the purpose of overload resolution, the functions which are introduced by a using-declaration into a derived class will be treated as though they were members of the derived class.
So, the using
declarations are legal, but the functions are peers in the same overload set, as you said, and the program is ill-formed.