Hi Margaret, I found an Arthur A. Aamoth b. 18 June 1940 who died 30 Nov 2003. His soc. sec. # was assigned in Oregon in 1956. Source: Social Security Death Index, Ancestry.
His obituary might say where he was buried. Check Random Acts Genealogical Kindness, raogk.org/oregon3.htm, read guidelines, choose Oregon, choose Lincoln county. All of this is based on the fact that he died in Lincoln County.
I checked FindAGrave in Oregon but they weren't listed there. It is not a complete database.
I didn't find Timothy or their sister.
Maybe the volunteer at Random Acts Genealogical Kindnesshas lists of whose in each cemetery in that county. Successful Searching!