Wanting to adopt my step daughter

Hello~ My husband and I were married in August of 2002. In April of that year his daughters mother was tragically killed in a car accident at the age of 22 years old; her daughter was 2. I am now looking to adopt my step-daughter as now every day I'm wanting her to be apart of me since I have I been raising her for the last year and a half. I'm wondering though where do I start? I'm not sure what to do as our situation is very different. To make the long story short, my step-daughters grandparents tried to take us to court after the death of their daughter to win custody of my step-daughter. They ended up settling out of court, but did make the comment that they never wanted me to adopt her. My husband and I believe different. If anyone knows of where I can start I would appreciate any help that I could get! Thanks