would be good to be able to choose who we alert planets to in the legion to help stop players taking ones when they shouldn't

if you cant trust your legion members you should prune them.

Agreed, kick the crappy stupid players.

Yes. In my former legion Warp Fleet, jacking a planet shared for someone specific was grounds for immediate kicking. If it is done after the recipient fails an invasion is another case entirely though.

For Phoenix Rising, the first case is left a warning. If they ever do it again they are kicked and all their planets are deemed "free for all."
If that wasn't enough, I also send out a legion announcement telling everyone!