You don't need ownership to relicense. You just need a license which permits relicensing, which BSD does (as long as the new license is compatible, and they usually are).
2. As the code is not relicensed you have to follow the terms. Generally for example even BSD licensed code (other than BSD0) requires that you include attribution both in source code and binaries or documentation, so you need to keep a full list of licenses and authors and list them out in the docs.