Your children's mother is also deceased, but she survived grandmother. Thus, her children will be dividing her share. You haven't told me what language in grandmother's will created the bequest to her children. If grandmothers will provided that it be divided among her children, and then also specified that if any of her children should die that their share shall pass to their child or children per stirpes (usually), then the children became errors directly rather than their mothers estate. The statue which requires the accounting to be filed with the court with copies to the heirs would apply to the children. And a direct beneficiary of an estate or trust has the right to question the executo or trustee concerning their actions. The children would have the same right as their deceased mother would've had and she lived until the distribution of the estate. This is taken directly from ORS 116.093 which I cited in my answer and it is very clear on exactly the question you have posted here:
(1)Upon filing the final account and petition for a judgment of distribution, the personal representative shall fix a time for filing objections thereto in a notice thereof. Not less than 20 days before the time fixed in the notice, the personal representative shall cause a copy of the notice to be mailed to:
(a)Each heir at the last-known address of the heir, if the decedent died intestate.
(b)Each devisee at the last-known address of the devisee, if the decedent died testate.
(c)Each creditor who has not received payment in full and whose claim has not otherwise been barred.
(d)Any other person known to the personal representative to have or to claim an interest in the estate being distributed.