-Your step-son is considered as your immediate relative (treated as your biological son), the same status as your wife, so you need to file a separate I-130 for him. This is different from non-immediate relatvies of US citizen, e.g. brothers/sisters of a US citizen, etc.
Thanks. But to me, this is out of a common sense: Brothers or sisters can take their spouse and children to immigrate together, but the immediate relatives - father, mother or spouse cannot. This could give better immigration benefits to brothers and sisters than to the immediate relatives and then treat them much better than the immediate relatives. How could the Congress make such a law? What is a rationale to make the law? This is why the I-130 instructions confuse me.