I think you will find that the bank want your parents to obtain advice independently from you. The reason for this is that the bank do not want to be in any way encouraging your parents to create a charge over their property or act as a guarantor in circumstance when it may not be in their interests to do so. By having taken independent advice they can assume that the full legal consequences of the guarantee and charge have been explained to them. In the bad old days a bank official would witness a mortgage by a third party(often a wife agreeing to put up her share of the house to secure the husband's debts). This stopped when the courts refused to enforce the mortgages on the basis that the legal consequences had not been explained to them and where it had clearly not been in that person's interests to sign the mortgage.
I don't think they want you to take independent financial advice, as you are not making an investment (except in your future, obviously!).