Legal Question in Civil Litigation in California

The issue is whether he really meant to change his separate property to community property or your separate property. You don't say so, but it sounds like he had no will, so if there IS separate property, heirs may be entitled to a share. With that amount at stake, you certainly should be hiring an attorney.

Your rights will depend on a number of factors: the terms of your husband's property; what constitutes community property during your marriage; the title on the deeds to the two properties; your husband's will (assuming he had one); his lawful heirs other than you (assuming there is no will); and possibly other factors that were not described in your question.

With this much at stake, you should be consulting counsel about your rights. This is especially true if your husband's sister has already retained a lawyer. There will obviously be an expense involved, but you need someone savvy who can protect your interests here. Your local bar association may have a referral panel; also search on line for someone who handles trust and estates litigation.