Appreciate that most students will be experiencing quite a high level of stress, frequently without any obvious indicators. Many fear that they might let their family down. Others fear that they will not be able to match the performance of siblings or relatives. There are also many pressures other than examination pressures. Appreciate that it is normal for people under pressure to become supersensitive and explosive from time to time.
Family members are usually the first targets.
Try not to overreact to such outbursts. Avoid confrontations especially over minor matters, like leaving lights on, leaving the lid off the toothpaste and not doing chores. Don't panic when they announce on the evening before the examination that they know nothing. Just do the best you can. We know you're giving it your best shot.