Advisor and co-advisor of PhD with different areas of research I did my graduate studies in Mathematics at two completely different universities, A and B, from my country. During my studies from university A, I had a very good professor X in theoretical statistics. In my studies from university B, I had a very good professor Y in stochastic calculus. Professors X and Y do not know each other and have not worked together before. Moreover, although both belong to a statistics department, their areas of research are not exactly the same. University A is good and is near my home. University B is top ranked and far from my home. 

In my country, opportunities of job at university for young researchers are little, so doing a PhD at two different universities would certainly enlarge my possiblities for a job in the future. My question is whether it would be acceptable to pursue a PhD at university A with advisor Y and co-advisor X. I mean, is it acceptable to do most of the part of the thesis with professor Y and some research with professor X, although both areas of research are not exactly the same, but both are from a statistics department?
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.