Granada does not have any English type restaurants like on the coast.
The best place to go is the Casa Lopez Correa
See website here.http://granadamap.com/casalopez/
It is a small restaurant run by an Englishwoman called Sue.
She is an excellent cook, she normally does Italian food but I am sure she will be able to make you something suitable for your father although I doubt if she can do meat and 2 veg. She does excellent Sunday dinners on Sunday.
There is a back room of the restaurant which is much quieter than the front part which would be the best place.
I advise you to phone her just to make sure she is open on the night you are coming.
If you go to the web site you can print a map of where it is and get the phone number.
There are lots of big supermarkets on the outskirts of Granada which are open till 10PM Monday - Saturday
If you come into Granada on the ringroad at junction 131 you will first see a big Carrefour Hypermarket and a bit further on a Lidl.
If it is after 10pm you will need a 24 hour shop.
See info herehttp://granadamap.com/detodo/