Use this forum it can help you. Good luck.

https://www.cfd-online.com/Forums/fluent/72873-connecting-two-fluid-zones-ansys-fluent-12-a.html

This condition is under discussion. Some researchers argues that  no-slip generates a  ill-posed system, mean while others have good results using that. But rarely they  are studying the same problem under the same conditions, so is controversy. I advice you read more about that to have a better vision about your problem

I agree with Ricardo - it greatly depends on the problem of interest. I used the non-slip boundary condition for all phases in different Euler-Euler granular models and the results were usually satisfying in comparison with experiments - it is a good starting point after all. If the outcomes of your model don't agree with validation experiments you still can modify the boundary condition, but I cannot give any recommendations about the spectularity coefficient.