Step-parent adoption questions...

Id like to move forward and adopt the 2 children I call mine, but not legally. I have been in their life for almost 7 years and married to their mother for the past 3.5 years. Their father passed away 5 years ago this month. Is the process difficult to adopt a step-child in a situation like this? There is no one to contest the adoption and we have records of their fathers passing including a copy of the death certificate. Is hiring an attorney absolutely needed or can I go through an online service and or get the forms and submit them to the courts ourselves? This adoption would take place in the state of South Carolina. Thanks!