-继母非亲生关系 is absolutely not the reason for the visa application denial. Your father and step-mother should show the evidences that they will come back to China after they visit U.S.
我父亲过去两次如期回国的纪录应该是很良好的。一旦再据,父亲今年估计又签不过来了。
选择2:让我父亲单独去签,来美后办绿卡。但不知道父亲可不可以以绿卡身份邀请继母来美 (他在美没有收入和工作)。父亲单独在美长期居住会比较不现实。我的目的就是想让父亲和继母每年都能来美小住但不用担心签证被据。
-Actually you can sponsor your father and step-mother to get the green card in China at the same time using Consular processing. Your step-mother = your biological mother from immigration point of view.