Got an Answer?
It depends on the situation and the ex. If my ex sent me a message after my parent passed away I would be appreciative, even though we are not on the best of terms and he was an asshole to me, I know it would have come from a place of kindness and compassion. Just as if it was his parent I would send him condolences. If it is that bad, it may just put salt on the wound though and make grieving harder for your ex. Just do what you think is right for the situation and keep his feelings in mind when doing it.
If you haven't messaged congratulations on having a baby or getting married then don't message now.
Not if you are no longer in contact, especially if you and his parent didn't really get along he may remember that and think your message is an insult. If you are ever talking again then say something.
Mind your own business
I was in this position 2 months ago. My ex lost his sister, very tragically. He and I were together 11 years ago. Ended on good terms. I ummed and ahhhed and decided to msg him via Facebook. He was very appreciative.
Not your family anymore! My brother’s ex wife who cheated on him turned up at my grandmothers funeral over Christmas because she loved my grandmother... but the general feeling throughout our family was it wasn’t her place... she decided to leave the family and you give up that right to the funeral when you are no longer apart of their lives especially if you haven’t had contact