As far as I know, BIS made ZAX which was the first 3d engine made in-house.
Nope, Reflexive made Zax, BIS had nothing to do with it. The engine was made by Reflexive. BIS publishes the game and added manpower, knowledge and QA and the producer.
Baldur's Gate was developed by Bioware and they made the Infinity Engine also. BIS again published that game and added manpower, QA and the producer. They got the engine from Bioware and used it in Planescape and the Icewind series.
All of the BG's were published by BIS, which itself is a subsidiary of Interplay.
