Crusader kings 2 title loss on succession

I've had plenty of them die in their 20s and 30s from 'stress' or some other equally ridiculous thing. My heirs though is a completely different matter. Well, my swedish kings tend to live to a VERY old age (in 3 kings so far I've had two live to their 70s, and the other king died in his 50s). That's like the unescapable fact of medieval life. Thus I lost my recently acquired land which had cost me 90 gold to conquer (mercenary warband).Д¬hildren die. Though he had a score of children, I hadn't enacted Primogeniture yet due to short rule. First game had my ruler die at the age of 19 with two children. I have had two games in a row where my ruler dies at a very young age. There is something wrong with Scandinavian rulers. What happens when he inherits? Does it matter which of his parents die first? I know I could solve this by making the Countess a direct Vassal by giving her the title to her own county, but I'm curious how it will play out if I don't. If I am right about that, her son would be both heir to the Duchy of the Isles through her, and the County of Desmond through his father. Presumably if I win the countess becomes the Duchess of the Isles, but as shes not part of my dynasty or a vassal (her husband is the vassal of a vassal), I think she would become an Independent Realm. So, I can press this claim in a War against Scotland. One of the wives of one of the counts of one of my dukes has a weak claim on the Duchy of the Isles, which I can now press on her behalf since the Duke of the Isles happens to be a child at the moment. However I've run into a tricky question with pushing a claim and inheritance, and I'm not sure how it will play out.

Crusader kings 2 title loss on succession