Hi Hannah, the first thing to say is that Google is not your friend right now - information on the internet about prostate cancer is not always reliable and much of it is American where things tend to be quite different. The second thing is that 'aggressive' does not mean what it sounds like - it is unlikely that your dad's cancer is racing off around his body as it tends to be quite a slow moving cancer.
You have mentioned the Gleason score as G7 on one side and G8 on the other. It would be really helpful to know the actual numbers - G7 will be either G3+4 or G4+3 and G8 will be G3+5, G5+3 or G4+4. Do you know which? They really make quite a big difference!
As hard as it is, there is little point trying to guess what the results of the scans will be and therefore what treatment options will be available. His PSA is high enough for them to have tested and diagnosed him but PSA is not a reliable way of guessing whether or not a cancer has spread, or how far. My husband was 3.1 and it had spread to his bladder (only a tiny bit and he is fine now), some people have PSA in the hundreds and no spread.
Once dad has had all the tests, a multi-disciplinary team at the hospital will probably review his results and make recommendations about what treatments are available to him. Unless it has spread, he will then have to choose which treatment he wants and that will be affected by which side effects he is willing to put up with or risk. You can help him prepare for this by downloading the toolkit from this website - it has sections explaining all the pros and cons of the different treatments.