Deceased heirs

I live in Oregon. I would like to know if my deceased sister's children are included as heirs to my mother's estate. My mother did not leave a will. I have been told that they are included, but I am looking for a second opinion. This would be under Oregon law. Thank you for any help you can give me.

Under the laws of all states (perhaps except Louisiana) the children of a deceased parent take a share.

What differs from state to state is how the law treats grandchildren when there are multiple deceased children who left grandchildren. Say there were 2 deceased children, one who had 3 grandkids and one who left 1. In some states the parent' share passes on to the surviiving children; in others it is allocated among all in that generation, equally. I do not know Oregon's law.