Terraria – How rare is the Blood moon in Terraria

Chances are they are spawning above you in the mine. Any kind of wall (stone or wood) except dirt will stop monsters spawning. I believe the walls are what stop monsters spawning unlike Minecraft's light level system.

If you've just dug straight into the earth, use the hammer to remove the dirt walls and replace with stone.

The other option is there is a blood moon on and the zombies broke through your house.

All of the comments you've received pretty much collectively give you the answer.

All of those enemies do spawn in 1.1.2; they're very rare, though, and require the right conditions/ biome to spawn. Water candles and battle potions will increase their spawn rate, but at the end of the day a lot of it is luck.

The groom spawns on the surface during blood moons, and Tim spawns at random underground (stone layer). Doctor Bones spawns in the surface or underground jungle at night, and more commonly during a blood moon.

So all you can really do is wander around, take advantage of the blood moons and of battle potions/ water candles, and hope for the best! You'll encounter them eventually if you keep at it.