My mother's sister married a man that had a daughter from a previous marriage. We never thought of her as "unrelated", she is a cousin. I mean, technically, the others are correct. Had my aunt adopted her (she raised her) then legally, I guess she would be a cousin. She still would not be related by blood, but she is my uncles's daughter, therefore my cousin.
My husband was not the biological grandfather to my grandchildren yet he was their grandfather. He spent quality time with them on a regular basis and they loved him dearly. He taught them how to ride bike, never missed a concert or recital. They brought him broken toys and he would fix them, "pop-pop fix?" they used to say. They lacked any attention from their bio grandfathers. I guess I have a different take on relatives, this is why I say if someone participates as a member of the family, accept them. Rarely, to we have opportunity to choose them.
These comments are a little off-topic and not the technical answer to the question asked. IMO There are situations when "step" no longer applies.