Stepfather is British, some questions about getting a British green card.

Your mother has been married to your stepfather for more than three years, and your stepfather applied, so your mother can obtain British citizenship as a spouse, and then if you are below 18, you can obtain British citizenship as a child, but if you are 2 1, and you are an adult, you cannot take refuge as a child. Because adults do not need their parents to bear the obligation of support and care.