the light of the sun will be seven times brighter, like the sunlight of seven days

"the sun will shine as bright as seven suns" or "the sun will give as much light in one day as it normally does in seven days"

Yahweh will bind up the breaking of his people and heal the bruises of his wounding them

Yahweh comforting his people and causing their suffering to end is spoken of as if he would put bandages on their wounds.