I am not licensed to practice law in Maryland, but in Washington it would be a pretty simple procedure. The adoption petition would need to be signed by both you and your stepson's mother. Her signature would be for the purpose of preserving her legal relationship with her son. Also, your stepson would need to sign a consent to adoption. Since he is an adult, you would not need his biological father's consent or a social worker's report.
You can find skilled adoption attorneys who are licensed to practice in your state at the website of the American Academy of Adoption Attorneys. I have placed a link to this website below.
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