Dear Great Man,
Welcome back to the Wefugees Community and thank you for reaching out to us again.
It is nice to hear that your company is so supportive and caring - really good!
Handbook Germany published some very useful information on this topic and more precisely on the "Invitation Letter" and "Declaration of Commitment for a Visitor Visa" (Verpflichtungserklärung). Please follow the link for details. I assume that your fiancée needs a declaration of commitment as well if she can not prove sufficient income/money for the trip. I can not share any experience or knowledge regarding companies signing the commitment for private visitors. I would recommend you to contact the immigration office directly to learn about the process and the requirements. Maybe my colleagues @mbeon-Éanna or @mbeon-Christine can add some information here as well.
In any case, please don't hesitate to get back to us with any further questions.
All the best,
Meike