Ggp was in context of W10 being the most expensive free upgrade ever, and it presumes possession of the Windows 7 license. So your comment is bogus on its face.
For both you and your sibling, normally W10 would have cost money as an upgrade, and it doesn't. If you had to do the math, what would it be? Not the cost of the original W7 license alone, and not the list price.
I contend that you paid for the work done to make 7 and you don't pay for the work for 10. Using them simultaneously is NOT the same thing, so invalidating your right to use 7, when you have used it for years, does not somehow mean you paid zero dollars to not use it.
I could go on, but the two of you seem great at choosing one thing to illogically disagree with and miss the point, so I'll give you no more rope to hang yourself with.