I bought electrical darts and used those on them, combined with EMP grenades and psi powers. It wasn't easy, I had to grind down in the cave killing those little hoppy things around the lake to get leather to sell to get credits to buy darts and EMP grenades, but the time I spent grinding also gave the shops a chance to cycle through goods, took a while. I needed 4 electrical darts, 3 EMP grenades, 3 high explosives grenades, and psi powers, and barely scraped through.