Legal Question in Real Estate Law in California

Not really a question about law; whether you could do a transaction (or pair of transactions) like this would depend primarily upon economics and, of course, your current lender's willingness to cooperate. However, I'd say the probability that this is a "do-able" plan is quite low, because you would need your financial capability up-front in order to make a down payment and obtain a loan on the new home. If you still have negative equity in your present home, I'd say buying a bigger (i.e., more expensive) home would require coming up with a bunch of cash from some independent source. However, don't take my word for it; ask a financial advisor, a real estate broker or lender representative who can look at your actual numbers.