Mortgage Loan Commitment and Intrest rate?

I'm trying to buy a house in foreclosure in California . Sellers contract says I have a financing term of 10 days to submit a loan commitment "by mortageg or deed of trust on the property. Agreement also says that once you provide that I can not change the terms of 'engagement' loan without the written consent MedlinePlus property sellers ... MedlinePlus Q : 1: I have already pre-approved . How long does it take to get a written loan commitment MedlinePlus MedlinePlus Q : 2: How to lock the intrest rate when I get the commitment ? What if intrest rates fall after the commitment to provide But before closing ? MedlinePlus MedlinePlus Q : 3: Am I responsible in any way if I get a commitment from a financial institution , but the sale is canceled for any reason and do not want to continue with obtaining the mortgage MedlinePlus MedlinePlus Your answers and help is greatly appreciated MedlinePlus thanks