Advisor and co-advisor of PhD with different areas of research
It is hard or impossible to answer such a question directly, not knowing the culture of both universities and the personalities of the two potential advisors. However, I can give advice about how to maximize your potential for a good outcome. 

Pick one of these advisors and universities and approach the person personally with your request to be a student. Either one will likely do. But pick the one you'd most like to work with if the overall plan doesn't succeed. First try to get accepted. Then broach the possibility of working also with the other professor and give reasons why you think it would be helpful to you and that you already know the person. If you get push-back on the idea, yield graciously. If the first person thinks it would be fine, approach the other, giving the current state of affairs and saying why you'd like to also work with him/her. You may wind up in the desired outcome. 

If the first seems hesitant to work with you at all, it is then time to approach the other as if it is a first request. 

Don't make it seem unnecessarily complicated at the very beginning. And don't worry about the (slight) difference in fields. It seems likely, in fact, that the two people already know one another. Distance is less of a barrier than it once was. 

Even better if you have any research ideas that might appeal to both of them. It might work out less well if you are depending on your advisor(s) to supply a problem. 

If you are working for one of these people then it might be possible for you to occasionally get advice from the other on a less formal basis, provided the person is interested in you and/or your research problem.