How to influence High Partition distribution
I am Emperor of Britain, holding all four kingoms, and I have three sons.
I want my player heir to get Ireland and England, and Scotland and Wales to go to the other two.
Currently, my player heir is getting Ireland and Wales.
If I grant Scotland and Wales to my other sons beforehand, does that stop them inheriting England, which will then go to my player heir? Alternatively, if I grant England to my player heir, they should also get Ireland (as it's my primary kingdon) right?
(and a quick aside: the order they're given out appears to be the order in which my line acquired them, right?)
Your heirs will inherit a set number of titles of each tier (Kingdom, Duchy, County). Granting them a title will count towards inheritance for that tier, so granting them a Kingdom prior to succession will change the title they will inherit. With High partition, three sons, and four Kingdom titles, you should keep two and lose one to each son.
An alternate way to ensure the right titles go to your heir would be to enact an elective succession on a Kingdom title where you can direct votes to your player heir. To do this, go to the title and click the "Add Laws" button. This takes the title out of the inheritance "pool" that determines how many each heir receives.
The Succession page on the CK3 wiki is helpful for understanding the various forms of partition. https://ck3.paradoxwikis.com/Succession