Both twins have made appearances in as NPCs (non-player characters); in the case of the Vax, the Champion of the Matron of Ravens showed up to save his lover Keyleth during the events of the Apogee Solstice.

Source: https://www.cbr.com/critical-roles-vexahlia-takes-aim-in-fantastic-cosplay/

Inworld AI’s technology goes beyond existing large language models and chatbots, allowing developers to power AI-driven non-player characters, bringing depth and realism to characters and rendering them within the logic and fantasy of their worlds.

Source: https://venturebeat.com/games/inworld-ai-raises-new-round-at-500m-valuation-for-ai-game-characters/