You did not yet tell me, where the library is, that you want to import. is it in your Pictures folder or on an external drive? If the library is not in your Pictures folder, copy it to the Pictures folder, then try again.
If Photos keeps crashing, when you try to import the library, there may be damaged video or image file in the library, that cannot be imported.
To avoid to import damaged files, you could try to open the library package and copy the folder "originals" out, then import in small groups from this copied folder.
Try this:
- Hold down the CTRL-key while you click the library you want to import from.
- Then use the command "Show package content"
- When the Finder window opens to show the folders inside, hold down the options key ⌥ while dragging the "originals" folder to the Picture folder to copy it there.
Now try to import small groups from the copied folder into your Photos Library, to check, if this can be imported.
Any file, that is not compatible with Photos8 should give an error message. Then skip it and try other files.