Section 3-3.4. Consequences of partly ineffective testamentary dispositions of

property to two or more residuary beneficiaries
    Whenever a  testamentary  disposition  of  property  to  two  or  more
  residuary  beneficiaries  is  ineffective in part, as of the date of the
  testator's death, and the provisions of  3-3.3  do  not  apply  to  such
  ineffective  part  of  the  residuary disposition nor has an alternative
  disposition thereof been made in the will, such ineffective  part  shall
  pass to and vest in the remaining residuary beneficiary or, if there are
  two  or  more  remaining residuary beneficiaries, in such beneficiaries,
  ratably, in the proportions  that  their  respective  interests  in  the
  residuary estate bear to the aggregate of the interests of all remaining
  beneficiaries in such residuary estate.