Ok if the trans is grinding going into reverse then you might want to look at how well the clutch is working. The input shaft has to come to a complete stop so when reverse is selected it engages with little effort, if the input shaft is still turning during reverse selection then gear will grind trying to engage.
As for the forward gear grinds, can be the same issue, clutch not operating properly, or a worn/cracked synchro ring.
Check and verify the master cylinder and slave cylinder are on and the hose line connecting the two. Bleed the system if needed.
But from what you say, its time for a tear down of the trans for full verification.