Losing a sibling of any age is hard, they were your playmate, best friend/enemy and the person that shared your upbringing.
The sudden loss puts them in a very high-risk category for similar actions, so be careful if you are the parent. They may feel they cannot talk about it as it’s stealing the limelight from the parents but they will need to.
It’s also important to not pretend the person that’s gone never existed, keep them in conversations as it helps maintain the relationship despite them not being here.
There are groups and online resources available and again talk to Doctors so they are aware of what has happened.