QB Issue Resolution:

Yes you can do it, keep track of each as a separate Class (using Class Tracking-only available in Plus) AND each company is reported under the same tax ID.

No, if each company has a different tax ID OR has different owners – different may or may not include your spouse, you would have to discuss that with a CPB

Resolution for Issue 'can I have two separate companies in one database?' available: Yes (Solved).
Source: Intuit Community forum.

can I have two separate companies in one database?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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