You've never been able to buy Windows; at least, assuming you don't have several billion dollars in the bank. It's always been available under licence. And the same is true of all software; even GPL software, which is licenced (albeit for free and with permissive terms) under the GPL.
"Owning" software might be a convenient short-hand for licensing software, but it's not a thing that end-users do, or ever have done in the history of computers.
In terms of your success in this endeavor? Precisely Zero. Not gonna happen. Microsoft getting people to move off Windows XP is a central part of its business plan for Windows. So while you can, of course, continue to use Windows XP yourself subject to the terms of your original licence - and you can run third-party tools to patch system components (via, say, Detours) for your and your friends if you want to, don't expect Microsoft to help you, or give you their permission to bring it to a wider group of people.