Interplay was the publisher. They stole royalties which provided the leverage for BioWare to buy itself out of the contractual onligations and publish NWN with Atari.

NWN being one of the first games to use master server and key technologies at scale was motivated to detect publisher royalty theft by tracking sold copies (and indeed an Atari division in Europe tried selling copies of NWN with copied keys) not just traditional piracy because the company had first hand experience with it.

Black Isle, an interplay first party studio made Infinity Engine spin off games which gets people confused here.

Source: Ex Bioware

BG 1 & 2 were definitely developed by bioware, interplay was the publisher. Interplay (black isle studios) developed icewind dale and planescape:torment, which were based on bioware's infinity engine. NWN1 was bioware and NWN2 was obsidian (came from black isle studios).

Source: memory and crawling through wikipedia articles

That's not correct. Interplay published Baldur's Gate, but BioWare developed it. See https://www.pcgamer.com/the-history-of-baldurs-gate/.

BioWare didn't make NWN2, that was Obsidian on the same Bioware engine that powered KOTOR 1 & 2 and NWN1.They did do Baldur's Gate 1 and 2 which were originally published by Interplay.