Hello Abhishek,
I tried both approaches with the following result :
Since I had already installed the website-app for me, I downloaded the second app from the Windows store. After the installation, the app opened and I was able to connect it with my wife's vault on the cloud space. Everything seemed to be fine until I closed the app.
Although the second instance showed up in the list of windows apps, I couldn't re-open this instance again. Every attempt to open it from one of the two desktop icons or from the start menu obviously always leads to the firstly installed website-app with my personal data.
At the end I gave up and added a second user for my wife in windows and installed the website-app using this login. Now everything is working as expected. To maintain my wife's vault, we have to log-in to our notebook with her account, but that's absolutely ok.
Thank you very much for your support !
Regards,
Wolfgang