第1个回答 2013-08-18
应该说有错：
人 be poor at
a sum后接定语从句they can't understand ,定语从句前省略了关系代词 that，所以，it是多余的。
take sb coming my home结构不符合习惯
Yesterday My aunt took two children to my home, they were poor at mathematics, so I taught them to do sums （that） they can’t understand.
第2个回答 2013-08-18
Yesterday My aunt took two children coming my home, they were poor in mathematics, so I taught them to do a sum they can’t understand it.
错误1.MY换成my，
错误2.coming my home，换成 to my house，coming做伴随语不顺
错误3.a sum they can’t understand it.语意不通，在sum 和 they 之间加上 but本回答被提问者采纳
第3个回答 2013-08-18
coming改作to come，sum 后面再接一个what，最后一个it不要
第4个回答 2013-08-18
Yesterday my aunt come to my home with two of her kids, who were poor in maths and need my help. Therefore, I spent a long time to help them to understand where they had been confused.
第5个回答 2013-08-18
应该不错吧，注意标点符号