Brothers and sisters Immigration

Situation>>: My mother and father married, had me and separated when I was still a boy; after this he had four children with another woman. My father died in 1997 without divorcing my mother. Both me and my mother are Us citizens, if I petition for them it will be about 11 years; so, since my mother and father never divorced I think she can petition for my half siblings as their stepmother; except for 2 responses I have found in the web; the responses I have received, (in-person and online) said that the definition of child in the law includes “.. a stepchild, whether or not born in wedlock provided the child had not reach the age of eighteen at the time the marriage creating the status of stepchild occurred.." and this implies a child in existence at the time of the marriage (see ad info)