account inaccessible

The most likely next steps are:

1. Start with the Sign-in Helper. It is the primary Microsoft flow for cases where the account says it does not exist, the password stopped working, or security codes are not arriving.
2. Since there was a passkey deleted email and the activity may not be recognized, go to Security basics and select Review activity. If an activity entry is shown that was not authorized, select This wasn't me or Secure your account.
3. If sign-in still fails, on the sign-in page select Forgot my password and then I think someone else is using my Microsoft account. Follow the recovery steps there.
4. If the account recovery path requires the Microsoft account recovery form, complete it from a device and location previously used for that account if possible. Microsoft states this can improve recognition of the request.
5. If the account has two-step verification enabled and none of the alternate verification methods are accessible, Microsoft support cannot reset it, send reset links, or change account details.
6. If the account has been inactive for more than two years, it may have been deleted and cannot be reopened.
7. For technical support, use Contact Microsoft Support. Support can route the case, but Microsoft states support agents cannot send password reset links or directly change account details.

Because the account was used by two people in different locations and a security-related email was received before access was lost, the most relevant path is to treat this as a possible account compromise and use the recovery flow immediately.

References:

• I can't sign in to my Microsoft account
• What happens if there's an unusual sign-in to your account
• Help with the Microsoft account recovery form
• Can I trust email from the Microsoft account team?
• How to check if your email address is a Microsoft account
• How to get a Microsoft account recovery code