In my family it is known that two brothers came to America from Ireland in the 1840's and I can source the ships they came over on, where they lived in America, all their children and when they died. However, the names of their parents are not known. How do I display them as siblings without creating an [unknown] father with just their surname and an educated assumption for a born before date for the parent? Is this the only way to link them as siblings? I've looked for the parents and hit a brick wall.