thank you very much for your request. I am a consultant at mbeon and migration consulting.
The granting or extension of some residence permits (e. g. for family reunification or for a permanent residence permit) is subject to the availability of sufficient living space. Sufficiently in this context refers to two factors, namely the nature and occupancy of the dwelling (size of the dwelling in terms of the number of inhabitants). Sufficient living space is usually available if
twelve square metres for each family member over six years of age
ten square metres for each family member under six years of age
living space is available and ancillary rooms (kitchen, bathroom, WC) can be shared to an appropriate extent. Children up to the age of two are not counted in the calculation of the sufficient living space for family accommodation. Residential premises that are used by third parties are generally not taken into consideration.
For Bavaria I would recommend you to inquire directly at the Ausländerbehörde. Since in Bavaria it is tested according to adequacy. The following list can serve as a guideline:
one person 50 m2
two persons 65 m2
three persons 75 m2
four persons 90 m2
each additional person 15 m2 in addition
Here are some links for your information: