You can handle this in one of 2 ways ... option 1 would be my preferred one ...
1) you will enter only the rental portion of the common expenses in the Rental section and indicate it was 100% rental and only depreciate the rental 1/2 portion ... the Rental portion of the RE taxes & mortgage interest will be entered on the Sch E and the balance later on the Sch A
2) you enter 100% of the common expenses in the Rental section and indicate that it is used 50% as a rental ... this way the program will put the rental section on the Sch E and the personal on the Sch A.
Either option requires you to review the entries carefully BEFORE you file the return.
You can divide the Real Estate Taxes between the two areas.
You will use the Rental Properties section to record the portion of taxes paid for your rented Duplex.
And then record the portion of taxes paid for your personal Duplex in the Taxes Paid section of your personal taxes.
Most Duplexes are equal sizes but should there be a difference in size you could allocate the taxes paid by figuring the approximate square footage.
Also, don't forget to include any other expenses and income related to your rental Duplex. I attached a link for information regarding rental expenses that you can claim on your tax return.