1) you have no need to worry . claim of hospital is barred by limitation .
2) even if facts mentioned by hospital are true what were they doing for period of 5 years .
3) under no circumstances sign any document admitting your liability to make payment .
4) if hospital had not been paid its dues it ought to have sued your father within period of 3 years .
5) in case any legal notice is issued engage a local lawyer and reply to notice .
6) if threats continue record the conversation and file complaint against hospital and person giving the threats for criminal intimidation