Not sure if this will help, but you should always install the earlier version of PS first. You might want to uninstall both versions and reinstall cs5 first.
On My Window 10 system I now only have 3 creative cloud versions of Photoshop installed. CS6, CC 2014 and CC 2018. I have set my Windows registry Photoshop.exe key commands edit and open to start CC 2014 my preferred version of Photoshop.
Using Windows Settings Default apps (Choose default apps by file type). I see I have set .jpg to be associated with CC 2014. I see I have not set my CR2 raw files to be associated with CC 2014 its associated with Photos. This has never bothered me for I always open CR2 files from Photoshop or Bridge and they use ACR to convert my RAW files into RGB images. However I had no problem changing .CR2 to be Associated with CC 2014. Now when I open a .cr2 file from file explorer if Photoshop is not running CC 2014 will start and it will use ACR to convert the RAW file to an RGB image. If Photoshop is running on windows CS6, CC 2014 or CC 2018 it will use ACR to convert the .cr2 file into an rgb document.
Problem has been solved by uninstalling then reinstalling CS2018. All file formats are now pointing to this program, so I'm now a happy camper.