Why do I have so many Doges?

I'm playing CK2 as a Merchant Republic, and somehow I've managed to create a second set of great houses. It is an Ironman game, so I can't go back to a previous save but I'd really like to get rid of the new set of houses. Do I have to murder a whole family (or would that just replace them as normal when you have five)?

I think I did it by winning a crusade for Andalusia and then giving a republic to my heir. I think that may have resulted in another set of Merchant Republic houses spawning, but I'm not positive.

Any advice on how to get rid of the extra houses or from now on is the competition for doge that much more competitive? I'm currently on patch 2.1.6 (TTXL).

Solution 1:

Ok, well I'm not sure of the exact cause of the multiple houses, but I can confirm that if one is completely eliminated they do not create another house.

Now, if you will excuse me I'm off to do some "house" cleaning.

After a bit more murder, it does look like I was able to set it back to 5 houses by murdering everyone: