1. This picture does not shown all (I adviced wireframe preview picture - not render). I'm not sure, if I see correct, but I think that most of pants is selected as "constrained group". Check in clothing room. Constrained should be only "belt"

2. Ground can reflect or gather light from objects. Go to material room, select ground and uncheck "shadow catch only". You can add reflection value node or create material which gather light.

Here you can find 9 links to threads refering lights and "gather"