I killed them all three times. Then there's no more demons spawn, the village is still growing.
I started the ritual, chunkloaded the center area. Killed the first demons and left. And I came back killed all demons later on that day. Next day, I came, and killed all the demons, and I got all the shards I needed, I left the place. This time I get to the place found out there's no more demons.

You can't mass exterminate them all. It'll eventually stop the village from spawning any more

Oh, that is a thing... thanks.