I suggest you have your grandson assessed by a specialist (educational psychologist / speech-language pathologist specialising in literacy) to determine whether he has any underlying learning difficulties. You could contact your local SPELD (Specific Learning Difficulties Association) to seek assessment and advice.
 

The information you have provided suggests your grandson would benefit from the program as you mentioned that he is 8 years old and has difficulty with sounding out words. Research suggests that an intervention approach focused on phonological processing skills and decoding (through a synthetic phonics approach), as well as work on recognising high frequency sight words and vocabulary development is most beneficial for all children learning to read. ReadingSounds 1 Pro incorporates activities designed to improve all of these skills. For more information about how the program works, please see:
 

http://www.readingdoctor.com.au/Movies.html

It is difficult to determine how quickly your grandson will progress without having ever met him...having said that, most children with difficulties in the areas targeted by the program make noticeable gains within a short period. The best way to determine whether the program is suitable for your grandson is to download the free trial and (after spending some time using the program yourself and learning about the various features), try it with him.

I hope that helps, and I wish you the best of luck in helping your grandson to achieve his potential.