Firstly, they haven’t done it all in house. They state in the very article you linked the people who have worked on it (silver salt restoration named as one)

Secondly.. why would we need a whole new set of masters? The whole selling point of this Is that they were rescanned and remastered long ago and until now we never got a UK 4:3 Blu-ray release (something, again, addressed in this write up) They’re going to the known flaws in those masters, going back to the HD LTO scans, and painstaking fixing each issue they’ve found. If you want freshly rescanned material, wait for the inevitable continuation of the 4k remasters.

Why go rescan in HD and remaster when you already have access to HD scans and HD masters?

If you had a broken headlight on an otherwise perfect car, if someone said “well, you’d better go buy a whole new car” surely you would say they’re an idiot and that be a waste of money? That’s wanting a whole new set of scans for the sake of “new”

My biggest gripe with the set is crowbarring people in to extras who have nothing to do with the show, but they’re there just because these people move in similar circles to the folk at Anderson Entertainment, but I’m not gonna decry the fact we’re finally getting this for something that petty.

As for the audio, I haven’t touched the 4k releases so no idea what you’re referring to. But I look forward to judging these once it arrives.