Hello, your father-in-law seems to have developed severe anxiety. Feeling highly stressed at this point of time is very obvious. Since he is an elderly person, reduce the amount of media exposure because there is too much covid-19 news. In these people get irritated easily and remains preoccupied with the negative thoughts. So he needs a lot of family support.
Next Steps
Immediately consult a psychiatrist/ clinical psychologist for a proper treatment.
Health Tips
Communicate with him, spend quality time and keep him engaged in different activities, and that might help in breaking the ice. Moreover, since online consultations are possible now, you can connect with any mental health professional from your comfort zone.