1. Both options would be viable. They can also use a combination if they like. Vines can form a netting if they have someone capable of securing it in place. It will prevent the larger rocks from falling. The vines are thorny, so working with them will be difficult but it would be possible. They can also consider climbing up and forcing the rockfall to slide in a controlled direction before removing the boulder.

2. They only need to remove one or two legs. It's sensitive to fire. Its legs are spiky, but underneath its protective hide the bones are weak and snap easily. You may decide between each other what injuries you would like to inflict on your characters as a result of this encounter!