Is a home study required for an adoption in California?

We have two foster children, twin boys, and want to move to adopting them. They’ve been with us over a year. We’ve talked to the social worker and she’s told us we may need to undergo a home study before an adoption could be finalized, even though the social workers come to our home regularly and see the conditions and how well the boys are doing. Is the study required for all adoptions and if it is, what is involved? The worker mentioned that it may include physical exams for my husband and me, fingerprinting, background checks, etc. We just want to know what to expect and how to be prepared, and how long the process will take. Also, should we have an adoption lawyer present with us for a home study to make sure everything is done correctly? We don’t want to do or say anything that could jeopardize adopting the boys.