If I delete photos from Pictures tisane space will they also be deleted from Photos Library?

First, are you running a "managed" or "referenced" library?

If you have a "managed" library deleting any image file in the Pictures folder will not be deleted from the library.

If you have a "referenced" library then deleting the image or source files in the Pictures folder will damage the library leaving you with only low resolution previews and thumbnails of those photos.

FWIW it's best to be running a managed library as referenced libraries have more problems.

Yes, that correct. If you have this checkbox checked in Photos' General preference pane

the photos are copied into the library and the original, source files remain where they were until you manually delete them.

What does "tisane" mean?