I dont think you can turn Viconia actually good ? You can turn Sarevok chaotic good, but the best you can do with Viconia is AFAIK true neutral. Also I think you have to romance her to archieve the later and I never did that, because she would leave the party once reputation crossed beyond 18.
I never figured out how to play BG2 properly as evil, or even neutral. My reputation always shot up to 20 very quickly. Murdering random innocents could bring it down but that was no fun at all.
Same here and since I prefer playing female characters, I never romanced Viconia, so she stayed evil in my games - I wasn't that surprised to have her evil in BG3 for that reason. Sarevok I once made good, but I never really used him in ToB, since by that, I have otehr characters levelled to my liking and used them more.
I get that people are sad if Viconia and Sarevok are their favourites and they put effort in getting them away from evil. Those two happened to be characters, I didn't use much, biut if they suddenly made Mazzy a serial killer or Jaheira a shadow druid for example, I would have been mad too. Though I do think, the possibility is always there when you worship Shar or Bhaal, since those two have a tendencie to mess with their followers a lot.
Still, it might have been better to leave them alone or make the tribunal judge an offspring of Sarevok for example and have the Sharran high priest be someone else and Viconia maybe an aquaintance of Shadowheart that makes a brief appearance (like Elminster with Gale for example).
I do think, I remember, that WotC made both of them caonincally evil again, but I blissfully ignored everything to do with Abdel Whatshisface, since I hated that my GW became canonical a human fighter, the most boring combination for me and I hate canonizing player characters (looking at you, Revan), so maybe someone more familiar with that timeline can confirm or correct me. Still, people liked their Viconia romances and having a redemption arc for Sarevok, so maybe I would have left them alone.
On the other hand, I fully expected Edwin to turn out to be Rolans new master, when playing early access.