I found a small NPC village during the early weeks in game with only 2 villagers. Long story short they both died. so after progressing into the game and got myself a blazing rod, made some potions and found and turn 2 zombies villager back to normal. they just like to stand around and do nothing. granted thats what they always do but even after expanding the village, add alot more houses and even more doors they still wont reproduce.