The FAFSA is used to determine if a student is eligible to receive a federal Pell grant of up to ~$5k. The maximum income level to qualify for a Pell grant is roughly $50k. However, a $5500 grant isn’t going to go far toward paying costs at CA colleges. Unless your primary wage earner has been living and working in CA since Aug 2015 your son will be considered OOS in Aug 2016, which means your family contribution will be the full $50k+ OOS rate. I believe that once he starts as an OOS student, it’s extremely tough, if not impossible, to get in-state rates at CA colleges.
Buying a house in CA in Dec. 2015 then flying back to Hong Kong to live won’t make your son a CA resident in Feb/March 2016. Even if he and your wife move into the home in Aug 2016, he won’t be considered a CA resident for tuition purposes. The family’s primary residence won’t be considered for financial aid (on the FAFSA), but if you own a home in Hong Kong then the value of one of the homes will be counted. If you don’t provide complete and accurate information on your applications then your son’s acceptances can be rescinded, his diplomas revoked, and he can face federal charges and deportation. Claiming to be a US resident while actually living in Hong Kong is the kind of thing that can get you into trouble. It’s not really worth it to gain a $5500 grant. And if your income is above ~$50k and/or you already own a home in Hong Kong, you probably won’t get that anyway.