请高手分析下句型

all they have to do 是句子的主语 他们所不得不做的
is 系动词
come and see the child 表语 来看看小孩
they want to bring up 定语从句 修饰child表示是他们想带大的孩子
所以句子主干是主系表结构 结合一个定语从句

all they have to do is come and see the child they want to bring up
1. all 主语(that） they have to do 定语从句 is 谓语系动词 (to )come and see the child they want to bring up 表语。
2.由于is 前有do, 所以，to come and see... 省略了to.
3. 他们不得不做的事情是来看看他们要抚育的孩子。

have to do是固定巨型 释为：必需做……
all they have to do可以看为一个整体，做主语
所以do和is不矛盾

all是句子的真正主语,they have to do是个定语从句,修饰all,这里的do 不是助动词,而是一个实意动词,表示"做"的意思.is是个系动词.come and see the child they want to bring up应该是一个从句,只是在这里省略了一些成份,而这个句子里又包含着一个定语从句,先行词是the child, they want to bring up作为定语从句修饰the child.

all 主语 they have to do 定语从句 is 系动词 to come and see the child 表语 they want to bring up 定语从句

all they have to do中do的宾语是all,所以与is不矛盾