Txmom2 answered your stomping ants question in her previous post. It is a random action.

Unless you use a doctor's consultation on each person (which can get a bit pricey) it's still possible they had a serious illness.

When you state that you fed them... did you stock the house with food, or did you simply have them prepare a meal? If there is not enough food to last overnight (with or without preparing a meal), there is the possibility that they can starve, especially if you do not pause the game.