I am not 100% sure but I don't think you want tanistry. Someone who is more expert level than me may say otherwise, but it really did nothing good when I used it before.
You also won't inherit 2 Kingdom titles I don't think, the only way of keeping the territory would likely be to form the empire of Britannia. When you die I reckon your new ruler will only keep 1 of them.
You also won't inherit 2 Kingdom titles I don't think, the only way of keeping the territory would likely be to form the empire of Britannia. When you die I reckon your new ruler will only keep 1 of them.