I'm worried about an inheritance. Our father will be receiving an inheritance and I looked up about an inheritance in California that there is no tax below 1.5 mil. But what happens when father gives portions to siblings. How much would we need to pay into taxes.

It will be considered a gift, he gets the money, so once it is his, does not matter where the money came from, it is now just a gift to you.

Agreed.

If your father receives an inheritance and then gifts part of the inheritance to others, then he may be subject to gift taxes. Depending on the circumstances, your father may or may not be able to "disclaim" a portion of the inheritance and not be subject to gift taxes.