Is there a word for your parent's significant other's children?
My mother has a boyfriend, he has kids. How do I refer to them in relation to me besides saying my mom's boyfriend's kids. My mother is not biologically related to her boyfriends kids.
Solution 1:
There's the term "prospective step-siblings", which implies a significant possibility that the parents will get married. You could also precede "step-siblings" with a variety of modifiers, such as "quasi", "pseudo", "para", "almost", etc. You could also apply modifiers directly to "siblings", either the above, or another such as "meta", "allo", etc.