“That failing any one of my five said children by death, the share or shares of the deceased, so far as remains unpaid , shall accresce and appertain to the survivors of my said children equally, or to the survivor, and shall become due and payable at the first term of Whitsunday or Martinmas after their respective ages of 25 years; and the trustees shall be bound and obliged to pay the same accordingly, with interest from the respective terms of payment, aye and until payment.”