>Mother, 41, kills her six-year-old twin daughters by shooting them in the head before killing herself in their Illinois home >Celia Henning, 41, and her six-year-old twin daughters, Makalya and Addison, were found dead on Monday >The woman's husband and the girls' father found them dead inside the bathroom of the home they live >Authorities haven't said if the mother left a note or revealed a motive