iphoto and photo

When you open an iPhoto Library in Photos, the Photos.app is creating a new Photos Library from your iPhoto Library. You are not seeing the "old iPhoto" in Photos; you are seeing, how Photos is trying to recreate your iPhoto Library in Photos. The old iPhoto Library is left unmodified, you can delete it or save it somewhere else. I have archived my old iPhoto Libraries on an external volume. occasionally I need them to recover the original file a photo or video, if it has become damaged later.

The new Photos Library will be recreating your iPhoto Library, as best as possible in Photos.

• All your iPhoto Albums are recreated as albums or smart albums in the "My Albums" tab.
• The events cannot be recreated in Photos, as Photos does not have events, only "Moments Collections, Years," in Photos 1 to 4, and "Days, Months, Years" in Photos 5 to 7. So Photos has recreated the events from your iPhoto Library as albums and folders, and is showing them under "iPhoto Events". You can delete this folder, if you do not want it. Deleting the folder will delete the albums inside, but the photos will remain in your Library. To delete the folder "iPhoto Events" ctrl-click it in the sidebar and use the command "Delete Folder"

Yes, if you delete the folder "iPhoto Events", it will delete the albums inside the folder as well, in one go, and the photos will remain.

Yes, they are just a folder / album structure recreating the events that were in iPhoto. Deleting those folders/albums will not delete the photos from the library.