Reverse will grind because there is no syncro. The pilot bearing may also be getting tight causing a drag on the input shaft.
Try putting it in 1st gear before going into reverse. This will stop the trans from spinning before putting it into gear.
On the second gear grinding, the 2nd gear is usually the first to have problems, speed shifting and down shifting causing it to get stretched out.
You could try some thicker oil to see if it will help, but first just try changing the oil if it hasn't been changed in a while.
If the oil won't help you will need new syncros.
