Legal Question in Family Law in Washington

If I were you, I would hire counsel for this because it's not going to be a simple matter. That said, what I think you should do is wait until you are married to your fiance. From there, you should contact the biological father, if possible, and explain where you are coming from, and ask him if he is willing to voluntarily terminate his parental rights, which would also include termination of his child support obligation. If he goes along, that makes it a much simpler and cheaper process.

From there, whether he agrees to do this voluntarily or not, you will want to file a petition for adoption. You'll need to hire a social worker to do a home study and give the court a recommendation as to whether to grant the petition and terminate the biological father's parental rights. If the case is contested, meaning the biological father will not agree to terminate his rights, you are going to have a tougher time, and the court is going to have to determine whether to terminate his rights.

I advise use of counsel since there are no standardized forms for this process, and even if there were, I think there are a lot of pitfalls for you to fall into that it would be money well spent to have a professional handle this for you. To that end, if you need a referral to local counsel, let me know and I am happy to help out with some names.