What is the Sharīʿah ruling on taking money from one's brother without his knowledge to meet needs and buy household items, and does this affect Allah's acceptance of prayers and supplications, and how does one repent from this act, and what is the ruling on being unable to perform night prayers despite attempts?

The door to repentance is open, and the inability to return the money to its owner, coupled with the fear of informing him, does not preclude repentance. You must turn to Allah Almighty to appease your adversaries on the Day of Resurrection, along with frequent seeking of forgiveness and good deeds. Those adversaries whom you can appease should be appeased, and those whom you cannot, the matter is referred to Allah Almighty with supplication and sincerity. And Allah, by His grace, will appease the adversaries from the treasury of His grace if He knows of sincerity in the servant's heart.