[Byrd]

There is another way to keep both of them.
Spoiler.
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Go with minsc to rescue Dynaheir, with out Edwin, and then have dynaheir attack a large group of gnolls. After she dies, Minsc will then stay with you if you drop her, go talk to Edwin and he will tell you that as your reward he will work with you. As for the keeping of the party together I recomend a cursed helm of opposite alignment for Edwin.