Karlin was a town not far from Stolin. The Chasidim had to flee to Stolin after being persecuted by the Misnagdim in Karlin.
If I am not mistaken, the Pinsk-Karlin Rebbe is the brother of the current Stolin-Karlin Rebbe.
As to the Havara – they have similar styles as Lubavitch, who also don’t have a Chassidish Havara.