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.
Neice or nephew no dummy its nephew
The boy is your nephew
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.
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