seeking daughter and son of my brother: Captain Lawrence O'Neil

Hello, I have very little information about the children of my brother, Captain Lawrence O'Neil. My brother died in 1990 at age 58. While he lived he mentioned that he had a Women he loved and two children. He spent time with the Montagnards and served three terms in the mid 60's He received the Silver star for leading Specail forces stride againist Viet Cong and North vietnamese in Nha Trang during the tet offsive of January 1968. I understand his women and male and female child left viet Nam to live in california. we would like to know if anyone has heard of him and if anyone can help us find his children and women. We come from a large family and would love to embrace our sister and brother. Peace and love, Julie O'Neil. If there is an organization that can help me please let me know.