When you say commercial I assumed you mean non-residential, therefore that property would not be a consideration for reporting. You report the residential property and you report the full loan amount.
If both properties are residential then you have the option to report both properties with unique identifiers and allocating the loan amount between them, or you can choose to only report one of the properties, and you would report the full loan amount.
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The opinions expressed are mine and they are not to be taken as legal advice.