If I can file a petition for my stepfather and how long will the process take?

You cannot petition for him. If he marries your mother, she might be able to apply for him.

Since your mother and him never got "officially married," he is not your step-father for immigration purposes and, unfortunately, you cannot petition him.

If your mother never married your stepfather, he is not legally your stepfather and you cannot petition for him. However, even if you could petition for him, if he entered the US unlawfully, he is not eligible to legalize his status within the US under the current immigration laws. Only if someone had petitioned for him under 245i would he be possible eligible. Please let me know if you have any additional questions or how I can be of further assistance to you in this matter.

You cannot file for him as your stepfather - you are too old for a step relationship to be formed for immigration purposes since your stepfather is not married to your mom. Plus he has other problems if he was not inspected when he entered the country.

Unfortunately, you cannot file a petition for your step-father because he did not marry your mother before you turn 18 years of age. Your younger sister can petition for him if he marries your mother before she turns 18. Does your mother have any legal status?