First question: If you [b]invade[/b] someone else you're pretty much hostile to everybody including people in your own covenant who also invade the same host. I depends on the other player invader itself, if he wants to attack you If you summon people, the only ones that can be hostile are the Mound-Makers(they've pinkish sign) Secondly: You can get boss weapons/rings from one of the Lords of Cinder located in Firelink Shrine. He's the little guy sitting on the second throne from the leftside. In order to purchase them, you must have the boss soul in your inventory, not already consumed.

Boss weapons are exchanged for their souls with the withered old guy in the throne at firelink shrine