Other than wishful thinking, i don't think it's possible these pairings would work out. Penelo and Vaan obviously have a very deep connection that could possibly evolve into a relationship in the future.
As for Ashe, well i don't think she would remarry anytime soon. Maybe to another noble of another kingdom (such as a Rozarrian prince or something). Balthier and Fran are pretty much always together although not in a romantic sense.
So yeah. My opinion is that the proposed pairings wouldn't really work out. Sorry to rain on your parade.
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