The majority of us have ancestors that immigrated to the United States. When finding the immigration record, do not assume that all of the children immigrated with the parents.
My husband’s grandfather immigrated with his parents when grandfather was a baby. With the parents, a list of children is on the manifest. After much research, it was discovered that one of the children was not the child of the mother – the mother on the manifest was the 2nd wife of the father. So, what was thought to be a brother of grandfather was the ½ brother of grandfather. And, also, another ½ brother immigrated before the rest of the family – in order to find a place to live.
Also, don’t assume that one sibling did not stay behind to take care of an aging parent or to take over the family farm. Or, maybe that sibling did not want to immigrate!