How to get onto the Liege’s Council

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.

As others have pointed out, essentially nothing. You may or may not be able to call him into wars, and he may or may not do the same.

Interesting thing happens though if you're an emperor-tier ruler and have an anti-pope installed. You gain a CB to install your anti-pope, and if successful can vassalize the pope (assuming you have a de jure claim or the anti-pope is of your dynasty, as usual).