Legal Question in Real Estate Law in California

The devil is always in the details. By putting you on title a presumption was created that any separate property interest was transmuted into community property, but that is a rebuttable presumption. What interest you have also depends on the source of the funds he used to buy his sister out. Often times one sibling will give up their share of other assets in their inheritance or use other inherited assets later, in order to take sole ownership of a piece of real estate. If he did that, then he just swapped one separate property asset for another. If he used funds earned during the marriage, however, then even if his original share remained separate property, the other half bought with community funds is community property. Lastly, even if both halves were acquired as separate property, and he can rebutt the presumption of commutation, you would be entitled to 1/2 of the principle payments made on any loan out of earnings during the marriage.