You have a couple of options, none of which are ideal or guarantee success.

• The most straightforward is to simply continue murdering the heirs until an heir of your choosing appears as the top choice in the election screen.

• Another way is to gain an electoral title in Scotland. Look at their de jure counties and try to snatch one in a war. Once you've done that you can nominate a candidate for the Scottish throne as well as see their second and third options for the heir, which can help with the murdering option I mentioned above

• Thirdly, if you are up for a major war, see if the brother you talk about has a heritable claim to the throne (weak or strong). Strong heritable claims are great as the children will be of your dynasty (matrilineal marriage) and have the claim. If you can't get them elected you can go ahead and press their claim. T

A nice addition to this is if you make your own kingdom also elective and then nominate the new king of Scotland (now of your dynasty if the above succeeded) as your heir. You can then join the two kingdoms together.

Considerations specific to kings/kingdoms as vassals

A kingdom with an active title will not de jure drift into your empire unless the kingdom's de jure empire title exists. (May have changed in patch 1.10)

Kingdoms have their own crown laws (crown authority, investiture), even when part of an empire (I am not completely positive, especially with patch 1.10, but that is what I have observed)

You cannot press de jure kingdom claims for your king vassals. The king can press his own de jure claims. You can press de jure ducal claims for your vassals, but not your vassals vassals.

Prestige. For a big enough kingdom (enough duchies) you would get more prestige from duke vassals than a king vassal.

Considerations similar to duke vassals, but amplified

Kings will want all territory in their de jure kingdom which will be bigger than a duchy.

With better marriage prospects, kings may obtain more powerful allies.

The increased power of kings makes them more capable to

• Rebel
• Conquer foreign territory
• Conquer other vassals in your kingdom