簡單的答覆是你們應該將你們想要的東西寫下來,然後在當地找一位處理家庭法的律師幫你們正式做一個正規的文件. 這是最保險的處理方式. 你們可以參考這個資料
http://en.wikipedia.org/wiki/Postnuptial_agreement
同時在加州你們要特別注意這個條例的規定
http://law.onecle.com/california/civil/1624.html
特別是這個部份
a) The following contracts are invalid, unless they, or some
note or memorandum thereof, are in writing and subscribed by the
party to be charged or by the party's agent:
(1) An agreement that by its terms is not to be performed within a
year from the making thereof.