本人刚刚起步学英语 所以想问些专业人士几个问题

本人刚刚起步学英语 所以想问些专业人士几个问题
1 the children go to school和they are going to school里为什么go要加ing
2 the children ususlly do their homework和they are not doing their homework里为什么do要加ing 是不是和第1个问题 一样的意思?
3 the weather's often cold in North 这句话的North前面是不是应该需要要加个the 还是可以不加 为什么?
4 Mrs.Sawyer usually stays at home in the morning 是不是可以变成in the morning,Mrs.Sawyer usually stays at home 这样是不是正确的
5 they are not doing their homework 能不能把 not doing 变为doesn't 如they are doesn't their homework 这样是正确的吗? 还是不能
6 they often drink tea together 中的drink 为什么不能改为drinking
7 he's reading an interesting book 后面能不能加at night
8 at night 和in the night 意思都是一样的 但是区别在那?
因为刚刚开始学 有这些搞不懂的位子 希望能得到大家的解决 谢谢大家了