Help me deal with backup bloat

Ok, so, computer kaput and I'm borrowing someone else's to write this.  We've got that covered.

I'll soon be sending the computer in for repairs, the mistake of not having my secondary close at hand will soon be over, so on, so forth.

This is ritual I know well.  My family, a family that got into computer-tech before it was cool,* is one that is computer kryptonite.  We never ask our dad for help when there are computer problems in spite of the fact that he'll know how to fix them because he likes being hands on rather than explaining from a distance and if he's even in the same room the laws of physics will bend in incomprehensible ways that will ruin everything in ways previously thought impossible.

As in:

"Why did we bother making this error message?  There is nothing that could possibly produce this problem within our universe."

"Witham."

My mother is largely immune because, even though she's still a Witham (she divorced my dad, not my aunts and uncles and cousins and grandparents) she was not born that way.

My sister and I were, but we're watered down.  We're as much Syska as we are Witham.  We grew up with our only regular quasi-religious tradition of any kind being "Polish Supper" which was when we went to a big communal meal at the area Polish church circa Christmas* and Easter.  (My mother's mother would occasionally drag us to Catholic church services, but there was never any regularity.)

Still, we're also as much Witham as we are Syska and that means we mix with electronics the same way water elementals do: badly.

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This brings us to the heart of the matter: I've needed to back up data for computer after computer after computer because --oh my fucking god-- only one outlived its warranty and most become irreparably damaged before the warranty has had chance to stretch its legs.

All of these backups take up space, and many of them duplicate things.

What I need, which may or may not exist, is a program that crawls a hard drive looking for duplicated files and folders (exact duplicates) shoves one version of the file into some "common" folder and replaces the files in the original location with not-exactly-shortcuts.

Not-exactly-shortcuts?  That's not a real term.  You just made that up.

Yes I did.  It needs to be more than a forwarding address, it needs to tell (almost?) anything that calls it, "no, do what you were supposed to do to me to that thing over there."  If something is supposed to read line three of the file named [something] at [place] I need it to not read line three of the pointer file that's holding that name in that place but line three of the original file the pointer file points to.

If something is displaying image files I need it to treat the pointer file for an image file as the image file its pointing to instead of going, "That's a shortcut, not my bailiwick."

So on, so forth.

Anything that can do what I need?  I'd appreciate the help greatly.

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* My mom was once a punch card operator and she was totally a programmer before anyone knew what that was, decades later when I was child, my dad was the one on the mono-molecular edge and my mom was still a force with which to be reckoned, even if my sister and I didn't really grasp that as children since, unlike our dad, she didn't work with computers for a living or a hobby.

* My little ceramic Christmas tree is something my mom won at a raffle at Polish Supper.