Translation:He ate eight big fish with his friend.
That's a good question about the position of grands, because it's an exception. Adjectives of size always go before the noun, except grand when you are talking about a person. Un grand homme is a great man. Un homme grand is a tall man. But as we are talking about fish and not people, the adjective of size goes before the noun. Regarding huit, remember you do not pronounce the "t" before a consonant, so it's a very short sound. If you listen a few times, you will hear it.