A: The typical way to gain control of his probate would be by initiating a probate, but, as you indicated, that requires a final death certificate.
The court can appoint a special administrator if there is something critical that must be addressed before a personal representative can be appointed (RCW 11.32 https://app.leg.wa.gov/RCW/default.aspx?cite=11.32&full=true). I would suggest you discuss this with a local probate attorney.
Powers of Attorney are only effective while the person who executed them is living. As soon as someone dies, the power of attorney ceases to be effective.
A: If your mom did not have a will, you would have a right to it before your nephew.
However, while your mom is alive, she can do more or less whatever she wants with her property. Likewise, she can leave it to whoever she wants in her will. At that point, you would have no right.
As far as who owns it now, the finance company does not control that. They also don't really get to choose whose name the property is in. That whole part seems odd. But, assuming your step-dad had a will, he could leave it to whoever he wanted. If he didn't, at least a portion of it would likely be your mother's. Absent a will leaving some portion of the house to you, you would have no interest other than what you might get eventually from your mother.
A: There is no requirement that your husband be aware of your will. But there are risks to a secret or surprise will. In the event you died and your husband survived you, he would be likely to open a probate assuming your old will or as if you didn't have one. If nobody brings the secret will to court, it would be like you never had it. Wills that are surprises are also potentially more likely to result in challenges to their validity. And, lastly, Washington is a community property state, so that impacts what property you can devise in your will and it gives your Husband certain rights with regard to community property.
I would suggest that you enlist the help of an attorney if you are considering doing something like this.
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