Section 10-6.7. Exercise by all donees; exceptions

Whenever  a power of appointment is created in two or more donees, all
  must unite in its exercise, unless the instrument  creating  such  power
  provides  otherwise.   But, if before its execution, one or more of such
  donees dies or becomes incompetent, such power may be exercised  by  the
  survivor  or  the  competent  donee,  unless such exercise is explicitly
  barred by the terms of the instrument creating such power.