Legal Question in Wills and Trusts in California

You are correct to point out that an inheritance is separate property. To keep its character as separate property, avoid commingling any separate property with community property. If your father uses money from a joint account to purchase the remaining interest in the property, the property could be considered owned jointly by the community and his separate interest.

Mr. Roach is sort of right. If your dad uses community funds to buy out your aunt, the community will retain rights in that money. So legally the house would be owned by your father as his separate property as to a 1/2 interest, and by your mother and father as community property as to a 1/2 interest. That doesn't really raise a commingling issue, since the separate and community character of the interests would be clear and preserved, unlike cash or investment accounts for example. So, in the event of divorce, your mom would own 25% of the house, or more likely, your dad would have to give her other communit assets to make up the 25%.