?我的问题是:
如果他的女儿已结婚(25岁)但无子女。是否适合上面解答的内容?
-No. Only minor (<21) unmarried child can apply for the immigrant visa together with the father.
如果不适合,如何(或有何方式)为他女儿家庭办移民?
-After the father or the mother becomes a US citizen, then he/she can sponsor the married daughter (include her family)'s green card. That will take a long long time (at least 30 years from now on)!!
Of course the daughter can seek other immigration method, such as H-1B to green card, etc. as most people do.