If e.g. a property is in joint names and the outcome of any settlement is to transfer it into one name, that is a property adjustment. Any money that is paid to buy one party out is a lump sum.
A registered charge is the same as a mortgage so the amount owed should be deducted from the value of the property to establish the net equity - which is the sum to be divided (although costs of sale may also be taken into account).
It is very sensible of your parents to have registered a charge. There can be no question that this is a proper loan. Unfortunately where loans are not properly documented they can be treated as soft loans, i.e. not intended to be repaid.