Here's a radical concept. In the unlikely chance that it comes up make a decision. Done.Yep.
Explain why Mysteries of the Moonsea and Sons of Gruumsh aren't consistent in describing who the city of Melvaunt's leaders are even though they were published lead than a year apart from each other. The only way to know which is closer to "authoritative" is to go back and read the 2e The Moonsea. A DM may not have time, access to the info to know which older products to look at, or the older products may also need to be adjudicated to get to ground truth.
If your players are casual, maybe not a problem. If your players are hard-core into the setting, it can lead (and has led) to disputes at the table.
In the case of succession, pick a likely NPC. Use a random name generator if you can't think of one. Make it an ex PC. Maybe the old king didn't really die and you have a fun side quest to figure out why he faked his own death.
It's your campaign, make it your own. You don't just run pre-published adventures do you? So you're already "making stuff up".