How can one overcome recurring negative thoughts, especially when going to sleep, which cause crying and insomnia, such as imagining the death of parents and the responsibility for siblings, knowing full well the love for one's parents and the unwillingness for any harm to befall them?

What you are complaining about stems from Satan, who strives to sadden the son of Adam. The cure lies in trusting in Allah and believing that nothing afflicts except by His permission. As the Messenger of Allah, peace and blessings be upon him, said: "Superstitious belief (tiyarah) is polytheism, and there is none among us but [has a flicker of it], but Allah dispels it with reliance [on Him]." You should put forth these thoughts and seek refuge with Allah from the accursed Satan. Remember that "the touch of Satan" is a promise of evil and a denial of truth, so whoever experiences that should seek refuge with Allah.

We also advise you to achieve certainty in belief in Allah's divine decree (qada') and destiny (qadar), and that what has befallen you could not have missed you, and what has missed you could not have befallen you. Know that Allah's choice for you is better than your own choice for yourself. This instills contentment and tranquility in the heart, and has great fruits such as peace of mind, reassurance of the soul, and an increase in faith.