The best Spanish grammar book ever is An Essential Course in Modern Spanish, by H. Ramsden, but it is admittedly a bit 'academic'. Because in Spanish what you see is what you say, ie there are consistent rukes for pronunciation, I suggest that your father reads the pronunciation rules and then listens to tapes again, very carefully and very slowly to see how they work in practice. The best way to learn how to pronounce a language (other than having a foreign national taech you face to face) is to read the rules, and then learn every phrase and sentence on the tape one by one. It's laborious, but start slow and gradually build up speed.
Buena suerte.