Yes, brother and sister married couples do exist, but they are extremely rare and generally considered taboo or illegal in most societies due to the close blood relationship between the individuals involved.
In modern societies, marriage between siblings is considered incest, which is legally prohibited in many countries. Incest laws are in place to prevent potential genetic and social issues that could arise from such close family relationships, as well as to uphold social norms and values.
There may be isolated historical or cultural instances of sibling marriages in certain ancient or remote societies, but such practices are not widely accepted or practiced today.
It's important to remember that societal norms and legal regulations differ across cultures and countries, so it's crucial to research and understand the laws and customs of a particular region before making any assumptions or generalizations. In the vast majority of modern societies, brother and sister marriages are not accepted or legally recognized.