With a hard link, if you delete the original, the link becomes the file. A soft link will not open anything if you delete the original but if you put another file back with the original name, the soft link will open it fine whereas the hard link is still the original file (just in a different place in the FS). But in both cases, as long as the original still exists, you can amend it via either of the links or via the original and all will be in step because the links point to the original. Another thing you will note is that the file size of a soft-link is 0b but the file size of a hard link is the same as the original (because it IS the original).
I generally find it much safer and better to use soft-links not hard-links as I think I said further up. Also, hard links do not work across filing system boundaries (e.g. different drives in Windows).
But either way, if you are creating a link from a master install to a 2nd instance, the link HAS to show the original contents - unless, in the hard-link case, the original gets deleted and then replaced.
Bottom line, use a soft-link and I think you will find that it works.