Complex sentence: Keish is today co-credited with making the gold discovery that led to the Klondike Gold Rush, although it was originally attributed solely to George Carmack, his brother-in-la possible that the discovery was made by Keish's sister Shaaw Tláa (Kate Carmack).
Split into simpler sentences: Keish is today co-credited with making the gold discovery that led to the Klondike Gold Rush, although it was originally attributed solely to George Carmack, his brother-in-law. It is also possible that the discovery was made by Keish's sister Shaaw Tláa (Kate Carmack).