Somehow, a while back, I got into reading about twins that had committed murder together. Here are a few:
Jasmiyah and Tasmiyah Janeesha Whitehead (Georgia, USA)
16 yr old identical twins. Murdered their mother by stabbing her and beating her with a vase.
Nathan and Justin Bawcum, 11-year-old twin brothers (North Carolina, USA)
They murdered their dad, and shot their mom and older sister. When the cops got there, their dad was dead, mom and sis were covered in blood, and the boys sat there playing with their rabbits. Given their ages, they got only 6 years and were released in ~2005. Not surprisingly, they have been in trouble with the law several times since then; not sure their current status.
Edwin and Edward Berndt (Texas, USA)
They are mentally challenged and lived with their 88 yr old mother. She fell one day and they didn't have any money to get her medical treatment so they left her laying on the floor. It took her 3 days to die. They lived with her corpse for 3 months, just stepping over her when they needed to. During those 3 months they never left the house and ate nothing but candy, chips, and popcorn. Given their disabilities, they weren't charged and were put under the guardianship of other relatives.