We have just come back from a trip to Cognac mainly to visit the Cognac houses. We only did the full tour of Hennessy which we had pre booked; it was really good and informative with a boat ride to take you to the exhibition and the barrels storage. It’s full of interactive sections about the area, the process, vines and the soil. You also get to see all the barrels in storage, and look for your birth year.
I would recommend pre booking tours as many closed between 12pm and 2pm may take an hour and are not all in English. We visited Martell also but did not take a tour.
We also drove over to Jarnac to Courvoisier but again due to timing could not take a tour.