Photos does not support to merge libraries.
You can only export the photos from one library and import them into the other library to unite your libraries.
1. Can I do this and not loose my Events and Faces
Photos does not have events, only moments, and moments will be created automatically.
If you want to safe the albums that Photos created from the iPhoto events, export the photos from each album separately and import them for each album individualy. Then recreate the album from all photos in the last Import album.
Faces cannot be transferred this way. When you export photos, you can as´dd the faces names as keywords, but you would have to recreate the faces thumbnails.