Q: Old photos on Icloud not deleting

It appears to be a similar problem as in this discussion - still unresoved  

Re: iPhotos keeps crashing due to photos

Try to select the bad photos without clicking them -  select a range by selecting good photos to the left and right of the bad photos.

If you cannot find a way to select all problematic photos to delete them, you can only download and save all photos you want to keep, then sign out of iCloud Photo Library from your iPhone or Mac, and use the option to to delete all photos from iCloud:   https://support.apple.com/en-us/HT204570

To turn off your iCloud Photo Library, follow these steps:

• On your iPhone, iPad, or iPod touch, go to Settings > iCloud > Storage > Manage Storage > iCloud Photo Library, then select Disable and Delete.

This will delete the photos after 30 days. During this time you can recover them.

Or contact Apple Support and ask the support team to remove the photos for you:    https://getsupport.apple.com