Same father is a MUCH more likely situtation in that society. Remember, muslims are allows 4 wives, IF they can support them. (Any other women in their households and beds are mere concubines, of which they can aparently have an unlimited number. Osama BL was, IIRC, the son of one of his father's concubines, a low status sort of thing to be)
That's true, but in Saddam's case, his father had died and his mother had remarried.
But as I see by later posts this in an expection to the general rule.