No relationship at all, you don't share a common ancestor.
step-granddaughter
Yes, you would be the step-nan (or step-grandmother) to your granddaughter's step-brothers.
step grandaughter is if your mums dad or dads dad marrys another woman that will make her your step nan and you would be her step daughter
Step-great-granddaughter
If she is your biological granddaughter (not step or adopted), yes.
Your Aunt. With Aunts and Uncles there is often no blood relationship howerver they are still your Aunt or Uncle. With step families taking the role of step Grandman, Grandpa, Cousins Aunts and Uncles it is more of what the individuals feel comfortable with. If her name was Beth, you could call her Aunt Beth if you were comfortable with it or just Beth is fine. If they were step sisters before you were born and the family is close then she would be your Aunt since birth and no step class is really recognized. If you were older when the marriage took place then a first name is fine.
Not sure but i guess it would be your great aunt's daughter
The word does not appear in many dictionaries, and is not a standard genealogical term. The usual spelling appears to be hyphenated as "step-granddaughter" rather than stepgranddaughter (as in stepdaughter and granddaughter) as seen in Wiktionary.
my step granddaughter Unless you are legally an adoptive parent of your step-son in which case she is your grand-daughter.
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.
If her son is from a previous relationship, then he would be your step-son.
Your daughter's step-sister would be your step-daughter.