"As soon as I saw my mother's face, I knew something was wrong. She was usually quiet when something was amiss. After seeing her concerned expression, I stood up quickly and asked her what was happening. She told me that she had been in an accident. I asked her earnestly what kind of accident it was, and she whispered that it was a car crash. However, she quickly came closer to me and told me not to tell my father. She was angry and disappointed because she had already had three car accidents last month and had spent a lot of money repairing the car. This was the fourth time this misfortune had happened to her. Suddenly, my father entered the kitchen and saw us discussing something angrily. "What happened, guys?" he asked us. My mother looked at me and then we both remained silent for a few seconds. The situation was extremely embarrassing. Finally, my mother started to talk to him, but my father interrupted her and spoke loudly. "Firstly, I have some good news: I won the lottery! I don't know how much it was, but it's more than enough for retirement," he said. After a few more awkward seconds, my mother told him, "It's nothing serious. I just sent the car to the mechanic because it was failing and making strange noises." My father responded, "Okay, I already have a mechanic that I trust. He will repair it tomorrow."

As soon as I saw my mother's face, I knew something was wrong. My mom in general used to be quiet when something was wrong. After seeing her concerned face, I stood up swiftly/quickly [you used the word "swiftly" correctly here, but the word sounds a little old-fashioned] and asked her, "what is happening?" She replied, saying she had had an accident, I asked her earnestly again, "What sort of accident did you have?" She answered, "a car crash," whispering (at the last). [<--- I don't know what you mean by "at the last".] Then she briskly came close to me and told me, "Please do not tell your father about this." She was extremely/very angry and disappointed about this issue. She had had three car crashes that month, so she had paid a lot of money for repairing the car. This was the fourth time that she had such an unfortunate accident. Suddenly my father entered the kitchen, and he saw us discussing an issue. He was angry. "What happened, guys?" he asked us. My mom looked at me and then both [both who? Your mother and father? If so, it would be better to say "they both"] kept silent for some seconds. That situation was very/much too/extremely/so embarrassing. After a while, my mom started to say something to him, but my father interrupted her, speaking loudly/shouting. "First, I have to tell you some good news. I won the lottery. Do not know how much it was, however, it is more than enough for retirement," he said. After some horribly embarrassing seconds more, my mom told him, nothing greatly serious, [<--- I don't understand the meaning of "nothing greatly serious".] "I sent the car to the mechanic. The vehicle was failing and making strange noises." My father answered, "OK. I already dealt with him before. He will repair it tomorrow."