Step Nephew
If her son is from a previous relationship, then he would be your step-son.
Your sister's son is your nephew.
Your sister's son is your nephew and you are his aunt (if you are female) or his uncle (if you are male.
step-granddaughter
The relationship of a stepbrother's son to someone would be that of a step-nephew. This is because the stepbrother is not biologically related to the person, but is a relative through marriage. Therefore, the stepbrother's son would be the person's step-nephew, as they are the child of the stepbrother.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
Neice or nephew no dummy its nephew
The boy is your nephew
Your step-son is the child of your spouse and another person, and is of no true genealogical relationship to you. So your step-son's children would also be of no true genealogical relationship to you either. However, they would commonly be called your step-grandchildren and you would be their step-grandfather or step-grandmother.
Your granddaughter and your sister's grandson are second cousins.
Yes, she did. She had the relationship of a mother that a mother has with her son. As most mothers do.
Step father and son