Q: Import photos to iMac without sync with My photo stream

Afterwards if I delete the photo from "my photo stream" folder it is deleted from everywhere.

Which My Photo Stream are you deleting from?  The one on the iPhone?  And why delete them from the My Photo Stream.  They don't take up any additional space on either device. 

If you want to delete the photo from the iPhone but not the Mac then delete it from the Camera Roll and not the My Photo Stream.

One way to do what you want is to  disable My Photo Stream on both your Mac and iPhone and download the photos from the iPhone to the Mac's Photos library by connecting the iPhone to the iMad via USB cable. 

The only way I know how to do what you want was described in the last paragraph of my first post.

Having the "my photo stream activated" in iPhone and iMac, how do I add photos in the iMac without being synchronised to the photo stream? If that´s possible!

It is not possible with Photos for Mac.  if you enable My Photo Stream to be able to download from your devices, the new photos you import to your Photos Library will upload to my Photo Stream.

That was different in iPhoto or Aperture, but Photos does not support it.

Now you would need two Photos Libraries, one that does not sync with iCloud and where you import your photos to, and one library to sync with my Photo Stream. But that would be very inconvenient, because you could not use your main Photos Library as your system photo library in other applications.

To import photos from your phone without using iCloud Photo Library or MyPhotoStream you either use iTune sync or Image Capture

Sync your iPhone, iPad, or iPod touch with iTunes on your computer using USB - Apple Support

Sync your iPhone, iPad, or iPod touch with iTunes using Wi-Fi - Apple Support

Image Capture: Transfer images and other items from your device

LN

iTunes Sync for Photos is not really syncing.  I find the name misleading, since it can only transfer selected albums to the iPhone, but not download from the iPhone

https://support.apple.com/en-us/HT201313

If you choose not to turn on iCloud Photo Library, you can sync your photos and videos manually in iTunes.

Sync your photos manually with iTunes

You can set up iTunes to sync photos to your iPhone, iPad, or iPod touch from the Photos app, or from a folder on your computer. Each time that you sync your iOS device with iTunes, the photos and videos on your iOS device will update to match the albums on your computer. If you have photos on your iPhone, iPad, or iPod touch that aren't on your computer, follow these steps to import them.

1. Make sure that you have the latest version of iTunes.
2. Open iTunes on your computer.
3. Use the included USB cable to connect your iPhone, iPad, or iPod touch to your computer.
4. Click on the device icon in iTunes.
   
5. Click Photos in the sidebar.
   
6. Click the box next to "Sync Photos." If instead you see "iCloud Photos is On," all your photos and videos are already on all of your devices that use iCloud Photo Library. You don't need to sync them through iTunes.
7. In the drop-down menu, choose the app or folder that you want to sync from.
   
8. Choose to sync all photos or selected albums.
9. Select "Include videos" to sync the videos from your app or folder too.
10. Click Apply.

You must import Slo-Mo and Time-Lapse videos through the Photos app or Image Capture in OS X Yosemite or later for their effect to be synced via iTunes. You can also sync Slo-Mo and Time-Lapse videos when you use iCloud Photo Library.

If you're syncing from Photos, only your System Photo Library is available in iTunes.