What should I do as regent for a toddler?

[Greybeard0815]

@ OP I see two options for you.

Option 1: Press your claim through war. Then kill the little sister and then the boy to inherit his remaining titles.
Option 2: Betroth and marry your heir to the duke's little sister and let her inherit by killing her brother. Then wait until your dynasty takes over peacefully.

 

[relaxed]

If you have steam, then search the workshop for sinstar87's wonderful mod that allows you to take control of the realm as regent, however it only works if your liege is emperor or independent king, with some tinkering you could make it apply to dukes.

The mod is called regent assume power.