You referred to a small business, in the singular, so I assume you are filing only one Schedule C as part of your Form 1040 tax return.
You should enter the whole amount of mortgage interest and real estate taxes when completing Form 8829 for the Business Use of the Home deduction. Based on your entries for the area of your entire home and the area devoted to business use, TurboTax will allocate the business portion of taxes and interest to the home office and move the remaining portion to Schedule A as possible itemized deductions.
