Install lsposed. Open your notifications and tap on the lsposed notification to open the lsposed app (there are other ways to open lsposed but I'm using this method). In the lsposed app, on the module section, enable Lucky patcher.
Now, open Lucky patcher app, tap on the 3 lines on the top left, there should be an option called "xposed settings". Tap on that and enable these options:
"signature verification status always true"
"disable .apk signature verification"
"disable signature verification in the package manager"
Now you can install apps with different signature over each other.