Incidentally, are all the Immortals in the Highlander universe supposed to be foundlings? I know that Duncan MacLeod and Richie are both stated to be so in the TV show, but what about others?
They are in the TV series continuity, at least. Like you said, both Duncan and Richie were, and in one of the novels based on the show Duncan explicitly said that all Immortals were foundlings.
I haven't actually seen it, but in Endgame
, isn't Connor MacLeod's mother strongly implied to be his natural/birth-mother, rather than an adoptive mother?