How can I perform istinja' from urine and feces using modern tools, knowing that I suffer from waswasah (obsessive doubts) and fear contaminating my hands, sinks, clothes, and everything touched by the water used in washing?

The most effective cure for waswas (obsessive whispering) is to ignore it. Water separated from a pure place after washing the penis or cleaning oneself (istinja') from feces is pure; it does not contaminate the hand, the sink, or whatever it touches. Ibn Qudamah said: "Water that separates, unchanged, from the place that has been purified by washing is pure." Likewise, if you wash the penis in the bathing area and the water separates pure and unchanged, everything it touches is pure. You should stop doubting the cleanliness of your family. If your brother leaves the bathroom without washing his hands, they do not become impure unless their impurity is confirmed. You must strengthen your bond with your parents and family and distance yourself from the waswas regarding the impurity of their utensils or hands, while advising family members who do not pray to observe their prayers.