You need to create the 3D models, extract the images, and import them as resources in your game. I would suggest to create sprite sheets for the animations.
Many 3D editors support setting the camera position parametrically and exporting images from that view point (which is useful, for example, when creating skyboxes). Although you probably will need to script that to do it bulk.
You could roll your own model viewer and script the required exports (there are 3D model viewer libraries you can use) and write the load files and export images from the camera positions you need in bulk.
There is actually some word on how those were done. Jason Regier, who worked on graphics for Myth: The Fallen Lords and was lead programmer of the sequel, has said:
In addition to creating the shipping product, we developed four tools to aid in the construction of the game. One utility, the Extractor, handled the importing of sprites and the sequencing of their animations. Another tool, dubbed Fear, dealt with importing polygonal models such as houses, pillars, and walls. (...)
The artists used Alias|Wavefront's PowerAnimator and StudioPaint on a single Silicon Graphics Indigo 2 to create polygonal models and render all the characters. At one point, the artists worked separate day and night shifts so that they could maximize their time on the SGI. Models were brought into the game using Fear, while the sprites were cleaned up in Adobe Photoshop and imported with the Extractor. (...)
-- Postmortem: Bungie's Myth: The Fallen Lords
Fear takes care of all the models; it is used to import the 3D rendered models into Myth.
-- Farkas, Bart (1997). Myth: The Fallen Lords: Strategies & Secrets. New York, NY: Sybex. p. 268. ISBN 9780782121407