The last time I brought both Karlach and Lae'zel I was a Draconic Heritage Sorcerer/ I had Karlach use the Greataxe from Sorcerers Sundries and Lae'zel used the Everburn Blade right up to the point she got the Githyanki Silver Sword from Voss.
My last run where I used Gale, Karlach and Shadowheart when I was a Pact of Blades/Battlemaster, Gale used counterpsell a TON, Because I'm not using Gale this time however, would multiclassing Shadowheart to get to level 5 Wizard so she can learn Counterspell be worth it?