Upvote:4
You can appeal and you can reapply. Appeals rarely work, unless the visa official made a math error with the available funds or the like.
If your brother is still an Iranian citizen, he has a right to travel to Iran and meet his father there. A right to a family reunification residence permit for the Schengen area applies mostly to spouses and minor children. There are a few cases where parents can get such a visa, but they require exceptional hardship.