Thank you for trusting JustAnswer with your important question.
Issues that we would look for in a sibling in this situation would be:
Depression - either that existed before the sibling died or that has worsened following the suicide
Increased risk of suicidal thoughts and attempts - this is true for friends, school peers, and others close to the situation
Anxiety or Guilt - fear that someone else will leave them suddenly or commit suicide, guilt over having "not done enough" to prevent the suicide, or guilt over "not know it was going to happen". Sometimes called "Survivor's Guilt" when they feel like they should be the ones who died instead of their sibling
Remorse or Grief - Remorse for not having a chance to say good things before the sibling died, and grief over the loss
Anger or Shame - Anger at the sibling for causing such pain and turmoil in the family, and shame or depression for feeling angry
Mood Swings - this is especially true as the survivor begins to have "good days" but then feels like they are not allowed to feel normal or happy yet because the family is still in mourning, or because they feel they shouldn't be allowed to have joy as part of the survivor's guilt
Withdrawal - the concern and attention from family and friends can be overwhelming, and the survivor may pull away from social contact in order to try to sort out their own emotions. This may increase their risk of self-injury, suicidal thoughts, and substance abuse as ways of "checking out" or "getting away from the pain."
Counseling and keeping a close eye on the child is highly recommended. It is also recommended that the parents seek counseling to help them cope with their loss, their own emotional baggage from having a child choose suicide, and helping them move through the grief in healthy ways so they can better repair the family unit for themselves and the surviving siblings.
A period of increased depression, withdrawal, crying, decreased performance at school, and other symptoms of normal bereavement or grief are expected. The survivor child may go through a period of denial where they appear to be fine, or they put on a mask that they are doing ok to protect the parents. Parents and school counselors are encouraged to keep an eye on kids immediately after the incident, 2-4 weeks later when the shock starts wearing off, and 3-6 months after the event when progress should be seen in normal grief. If the symptoms continue to worsen, or do not show signs of improvement after that time, counseling and medication may be needed to help the survivor child move forward.
Hope that helps,