Your biggest city is where the kings heirs will appear, but it is not a capital as such and there is no "distance to capital" factor in MTW. In MTW distance to faction leader is what counts and this affects the loyalty of provinces only.
To increase the number of heirs you have, ensure that your existing heirs are married as soon as possible, this way they are producing heirs before they even get to the throne. If you're lacking in marriage proposals or other factions keep turning you down, then you will probably have to marry your heirs to your own princesses.
Bookmarks