So I recently set up Boot Camp on my MacBook, and I am in desperate need of space. I have disabled iCloud Photo Library, My Photo Stream and iCloud Photo Sharing. There are still photos on my MacBook in the Photos app, and I am wondering: if I delete these photos, will they be deleted from my other devices too?
Once all iCloud photo sync features are disabled (iCloud Photo Library and photo stream) pictures will only be deleted locally. Generally, unless you have disabled this prompt, Photos will warn you if you are deleting a picture from a Cloud location.
If you want to view your photo library online, you can always go to http://icloud.com/#photos to view them.