Because your son was married and had a child at the time of his death, his wife would have to file a wrongful death claim. Any settlement gained from the lawsuit would be for the wife and child that he left behind. This amount would be meant to cover funeral and burial expenses, healthcare costs and potential loss of future earnings if he was working and/or supporting his family. His child may also file a claim and receive a settlement for the loss of the parent-child relationship.
There are certain circumstances, in which parents can file a claim on behalf of their adult child, but the child must not be married or have any children. Had this been the case and you were financially dependent on your son at the time of his death, and could prove that he was the main source of income in your household you would be able to file a wrongful death claim on his behalf. It is best to speak with an experienced Seattle wrongful death attorney to get more information about filing a claim.