A MUM and her three children were murdered by her sister’s ex when he torched the family home with an accomplice, a court heard. Bryonie Gawith, 29, Denisty Birtle, nine, Oscar Birtle, five, and 22-month-old Aubree Birtle all died in the blaze in Bradford, West Yorkshire. Her sister Antonia Gawith managed to escape the fire,…