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it may be possible. you can begin by contacting your local child protection services and explaining why you beleive your grandchild is not in the best environment. they will investigate and then you can file in the courts for a guardianship. it will be very helpful to have the CPS do the investigation to help support your claim against the parents being inept and not in the child's best interest. you, of course, could consult with a local attorney to help you with this matter, too.
you can begin with the CA child protective services and they can place you in contact with someone in Oregon. you also need to file in the homestate of your grandchildren. so if they live in Oregon for at least 6 months, then you need to file there. if they have recently moved to Oregon then you can file in your county in CA