I had similar experience. One referee is my mentor's former student. Therefore, it says in his CV that he graduated from the same university that I am in. But I didn't have any other choice at that time. Therefore I submitted his letter for my RFE and my case was approved very quickly.
My suggestions are:
1. If you can find some more independent letters (1-2 is enough), you might want to try. Even it might not help, it is important for you to be confident in your RFE response.
2. You might also want to put some other letters before these two letters when organizing your materials. My experience taught me that INS officers don't look too deep into materials, especially if the materials are not the front page. Therefore, you can put the best reference letter on the top,i.e. some letters which can not have any tie with you, followed by these two letters.
3. In your coverletter, stress on the point how these people know your work, insteading only focus on them as independent experts. For example, you can say" Dr. XX's work is widely acclaimed by the scientific society. For example, someone further his research based on Dr. XX's finding. Someone else, who is the editor of some book in which Dr. XX is one of the author, comment on Dr. XX's work as following:---". Your impact in the field as a whole is really the thing that INS officers are looking at. Therefore, the opinion from your citation and editor is very important, no matter whether you could have some distance relationship with them.
Therefore, based on your RFE, I think these reference letters should be fine, as long as you deal with them with caution. If possible, you might want to get some more. But if that is all you can get, that is still very good. Don't worry too much. You just have to get the best you could and you have a good chance of success.
Good luck.
My suggestions are:
1. If you can find some more independent letters (1-2 is enough), you might want to try. Even it might not help, it is important for you to be confident in your RFE response.
2. You might also want to put some other letters before these two letters when organizing your materials. My experience taught me that INS officers don't look too deep into materials, especially if the materials are not the front page. Therefore, you can put the best reference letter on the top,i.e. some letters which can not have any tie with you, followed by these two letters.
3. In your coverletter, stress on the point how these people know your work, insteading only focus on them as independent experts. For example, you can say" Dr. XX's work is widely acclaimed by the scientific society. For example, someone further his research based on Dr. XX's finding. Someone else, who is the editor of some book in which Dr. XX is one of the author, comment on Dr. XX's work as following:---". Your impact in the field as a whole is really the thing that INS officers are looking at. Therefore, the opinion from your citation and editor is very important, no matter whether you could have some distance relationship with them.
Therefore, based on your RFE, I think these reference letters should be fine, as long as you deal with them with caution. If possible, you might want to get some more. But if that is all you can get, that is still very good. Don't worry too much. You just have to get the best you could and you have a good chance of success.
Good luck.