I don't if you've ever thought about that, but maybe you could use the existing voice acting? My point is, there are hours of Geralt/Dandelion/Triss talking and CDPR have probably even more records, so maybe you could just cut the existing acting, paste it where you need it, sync it and polish it in order to avoid the voices being too flat? I don't know if it's even possible, just my two cents.