How I do I merge two Photo libraries that were updated from iPhoto?

I was forced to use multiple libraries with iPhoto. I want to consolidate them all now that I have started using the new Photos. How can I do this without losing metadata or passing them thru Aperture?

Unfortunately there's no easy way to do this. There is paid software like iPhoto Library Manager that will allow you to merge multiple libraries, but nothing built into the new Photos app will let you do this without sacrificing metadata.