I am no lawyer but an ordinary law student to be clear, i will try to provide some insight about your problem.
1. since your father has retired and since there are notices sent to him, the creditor may ask for attachment of property in court, but considering his state of health, your father may ask for loan restructuring with his creditors. In case your father die and if there are properties they can ask for the attachment but if there are none, then the loan is already extinguish with the death(god forbid)of the debtor(your father), assuming there are properties left but the value of the said properties are not enough for the satisfaction of the loan, the creditors can no longer ask beyond the value of the property.
2. Notice sent by the creditors. Legally speaking, this is done to put your father in a legal default, that means, the debtor can not use as a defense 10 year prescriptive period provided by law if the creditor failed to demand payment of the said loan. This is essential as far as court proceedings are concern. since your father is already incapable of paying the said amount, it is up to the creditor and debtor to come up with a compromise agreement.
The creditors cannot compel you to pay for the loans obtained by your father, since loans are not transmissible to the heirs of the debtor.