Honestly, you should prioritize yourself first and foremost. If you exhaust yourself trying to be there for everyone, it will take a toll on your mental health.
You can choose when you feel mentally capable and engage in conversation. You can ask them if they are okay, and if they need to talk. You or them do not have to share everything, only stuff that you and them are comfortable about sharing.
Sometimes you can go for a neutral topic, discuss about hobbies or interests, or share tips regarding things you can do to improve your mental health.
Hope this helps.