Do listen to them and try to benefit from their knowledge. Victims often complain and feel they are being treated unfairly. Don't try to become their protector. Do ask them for suggestions to improve the situation. They need practice giving positive ideas.
Sarcastic types use words as weapons, often destroying harmony in a group and causing resentment.
They can be poor team players. Don't let them get away with this behavior. Let them know that sarcasm is unacceptable. Do compliment them when they say something positive or show team spirit. Nay-sayers have nothing good to say about others' ideas.