File adoption paperwork

I am looking for assistance with filing adoption papers for our family. I have two children by marriage that I would like to become the legal guardian for, my wife and I are hoping to have this processed quickly and see no challenges, as their biological father has passed away over 3 years ago. I have a daughter who is 1+ and a son that is 17, please let me know if you are able to assist in this matter moving forward. Thank you

I understand as one of the kids is over 18 its purely to "formalize our relationship" but I would still like to move forward in the process for both

Experience needed:

Submitting/filling adoption paperwork

Familiar with adoption process when one parent is deceased