Final answer:
In this situation, the interests involved are Owner A's life estate, the sister's life estate, Owner A's reversion, and Owner A's children's remainder.
Step-by-step explanation:
In this situation, there are several interests involved: Owner A has a life estate interest in the house, which means he has the right to possess and use the property for the duration of his life. The sister has a life estate interest in the house for the duration of their mother's life.
Upon the mother's death, Owner A has a future interest in the house called a reversion, which means the possession of the house will return to him.
If Owner A has died before the mother, his children have a future interest in the house called a remainder, which means possession will go to them according to the terms of his will.