请问有专业的英语老师告诉我一下的定语从句哪个有问题，是什么问题，谢谢！

Question

1，The house on the left which has two windows is mine。2，That man is strong who is my brother。3，my brother has one girl who is his sister。4，He is a student in my school who often helps others。5，Children work in their holidays who gain some valuable experience。就这5个句子，谢谢！

Answer 1

第一句没问题。
2、有问题。定语从句是跟在名词或代词后进行修饰的，你这句话修饰strong了。应该是:the man who is strong is my brother.
3、感觉这个句子本身有问题吧，什么叫“我哥哥有个女孩，那是他的妹妹”，不懂这个表达，这是很牵强的硬要扯上定语从句吧。
第四句没问题
5、有问题，和第二句类似，你这个从句是修饰children的，应该把它直接放在children后面。children who work in their holidays gain sone valuable experience.

Answer 2

第二句把who之后的定语从句提到先行词The man后，否则句子松散。
第五句把引导词who提到children和work中间，让gain作句子谓语。这样句子翻译才通顺。

Answer 3

最后的句子有问题。应该说children who work in holidays gain some valuable experience. 把意思弄错了。另外定语从句最好放在俢饰词之后。第三个句子我没看懂