What is the output you receive when trying to do the above? i.e. do you get high numbers (double counting), do you get an error or do you get duplicates etc.
If you are receiving high numbers then check the deteminants you have set in the Query Subjects.
Are the fact tables and query subjects at the same granularity?
Stejawh's solution should work but if the DW and FM are correctly structured then there would be no need for Stejawh's solution. Correct me if I am wrong Stejawh, but there should be limited need to perform joins from within the reports because if the DW and FM are structured correctly you can achieve the creation of more-or-less any report.
On a side note, you will find that joining two fact tables directly breaks all the laws of good data warehouse design, and more importantly, the best practices of Framework Modeling.
If you want to know more about ETL, Data Warehouses and Star Schemas, I recommend the web site and books by Ralph Kimball.
It is important to follow DW best practices. I have found them very counterintuitive and sometimes even in violation of the best practices I've used for years in DBMS. But, when you follow the DW best practices, and set things up the correct way, it provides great ability to produce just about any report you want against your measures quickly and easily. The leverage return on the investment of setting up the DW correctly is well worth the effort.
