There is any footpath from Grange to Rosthwaite? ( Borrowdale jaws )
you can follow the old corpse track as far as the old slate quarry and drop down to
Rosthwaite or follow the river, I would guess about 20-30 minutes. There are 2 cafes in Grange and the track out is after the café that is not next to the river.
If you fancy a climb Castle Crag is on the way adjacent to the path and well worth the effort - it is only 200mm of climbing but a rough steep path.
Views are great , and there is a war memorial plaque at the top.
Yes, you have a choice of routes, and it's a really beautiful walk either way. You can pass either to the east or to the west of Castle Crag (and as rarrar says, it's well worth a little detour to the top: one of the smallest fells in the Lake District, but with great views).
I would suggest making sure you equip yourself with one of the 1:25000 OS maps so that you can check out the routes for yourself.