You'll need what's called a Master Project.
Unfortunately, you're well under way and converting to this will cause you some pain but here are the basic steps.
1. Tidy up. Open each of the two projects and make certain the Resource names are exactly the same in both projects. Save the updated files.
2. Build a resource pool. Open a blank project. Put all resource names in this project. Do not put any tasks in this project. Save it.
3. Build the master project. Open a blank project. Click on Insert | Project. Navigate to the file in step 2 and open it.
3a. Add a sub-project. Click on Insert | Project. Navigate to the first project you are putting into the master project. In the Open File dialog display, make sure the box "Link to file" is checked. When the project is open click on Tools | Resource Sharing | Share Resources. Click on Use Resources From and select the file from step 2; click on "Pool takes precedence".
3b. Add a sub-project. Repeat 3a for the second project.
4. You *may* (it's been a long time since I've had to build a master project and I can't remember exactly what happened and what I did) have to fiddle with each resource so that you eliminate multiple same-resources in the sub-project files. This may cause you to lose some of the Actual data (if you are tracking it).
As a "heads up": there have been some comments that, on occasion, Master projects are compute-resource intensive. Others have not experienced that phenomenon.
