Imo the monuments in fallen gate did nothing good to the lore, they work against 1. liege names 2. thex relation between high and dark elves 3. age of cristanos(dev stated that she is incredible old) note that all 3 points are eq2 lore, not stuff from anyother eq game or p&p
Solution1.: Maybe those monuments refer to rulers of other citys in the underdark, not to rulers of neriak(would be very strange..)
2.The original king and queen were Thex and in sometime of Neriaks history other rulers defeated the house of thex without eliminating all of them, so they came to power but later thex ruled again.
Possible that Cristanos is the orignal first queen and survieved during the reign of the other rulers.