Since I've been asked, here are the details to answer regarding the conundrum of Genesis 10:21 "To Shem also, the father of all of the children of Eber, the elder brother of Japheth, children were born."
Is Eber an elder brother of Japheth, making him a previously unmentioned fourth brother with Shem, Ham and Japheth? Was there some kind of Levirate marriage going on wherein Eber, the eldest, died and Shem took his wife and children for himself, in effect stealing his lineage?
Actually, the answer is much more simple than that, and this will reveal one of the dangers of the more literal translations (which I am still in favor of). In Hebrew the word "av" means both "father" and "ancestor." It is a type of usage which also exists in English. "ben" (or its plurals) can mean both "son" and "descendent." This makes the count-the-people method of determining biblical dates somewhat flawed. When you go from one generation to another there can be skipped generations. And then if two different biblical writers decide to skip different generations in their lists, then you end up with two lists that don't match. But that wasn't a problem for them, because they all understood that a "son" (direct heir) could be meant or a "descendent" could be meant. Not a big deal.
So here, Shem is the "father" (ancestor) of all of the children of Eber and Japheth's elder brother. Shem is listed because he is the beginning of the line after Noah. Eber's sons are listed because Eber's line is the most important (10:25-29). Eber gives birth to Peleg (who has one claim to fame) and Joktan, from which the godly line continues.
In this section the lines of Noah's three sons are given in reverse order of importance, and it would be helpful for the translators to have section heads that say at verse 1, "Noah's Sons," verse 2 "Japheth's Sons," verse 6 "Ham's Sons," and 21 "Shem's Sons." If you look at the whole section with that knowledge, it should come into focus.
There is an "art" to how biblical writers constructed genealogies and presented them and we tend to pay little attention to that (including me!) and so we often miss "the point" and end up confused or we quickly rush through reading them until we get to the "important" part of the narrative.
Kudos to Noah and Miriam for reading carefully enough to catch this!