You only have to install Thunderbird once. Use different Windows user accounts for everyone using the computer. This way everyone has an own Thunderbird profile with all the configuration settings and mail.

This answer doesn't solve my problem. My wife and i wanted to use one Windows account. So I think i have to use Windows mail and my wife Thunderbird. It seems not possible to install Thunderbird twice in different maps.

My wife and i wanted to use one Windows account.

Up to you, but certainly not recommended.

You can create multiple profiles, and then start Thunderbird with the desired profile. That means Thunderbird is only being used by one person at a time. Even though Thunderbird can be started more than once, so that two people can use it simultaneously, but with a different profile each, you'll almost certainly screw up things. Hence this is not recommended.

In any case, there is no point in trying to install the same version twice, and then run it simultaneously. Good luck.

Thanks a lot!