Jeez, this is a good question. We’re going to get philosophical for a minute.
There is nothing preventing a family from writing a critical obituary. However, we would argue that an obituary is not the place to air grievances and point out faults.
After all, no one is perfect. Some people are downright rotten. And it stinks when the rotten ones are in your family. But an obituary is not a report card of how that person treated you and other family members.
An obituary should be the full story of a person’s life. If you are asked to write an obituary for someone and you have nothing nice to say about them, it is perfectly acceptable and wise to refuse to write it. Instead, allow someone else who might have had a different relationship with him or her to write it.