Random Creepers Spawn In My House

So as me and my brother (we play on his world often)are standing in our house or moving around doing things, a creeper would spawn out of nowhere in our house. Most of the time, we're busy in chests or furnaces to see our surroundings so they've exploded quite a few times. We tried placing torches just about everywhere inside to prevent spawning but that doesnt work. We've had to evacuate the house as to make sure it doesnt explode. Most of the time as soon as we look back inside it already despawned. Only once did we end up luring it out and shooting it down. We would really appreciate it if you guys could fix this issue because it's risking both of our lives and valuables. Thank you so much!!!