Responses

No, in the original story, the grand duke couple was saddened by the death of their previous kid, so it's more likely that they might not be blessed by anothet heir, so their lineage would have been cut off there and another child from vassal family might have inherited the dukedom.
But with the blessing of child they got from this timeline and all of Louise and friends had done and would do in the western continent, might change the power structure in the western continent more than the original should be.
That child of the Archduke and Archduchess is the ogml hero?
Btw this is not a spoiler but a speculation...
Besides, that would explain why their first dungeon is that hero Valencia's tomb....