as long as you did not cash out refi; just add the two 1098's together.
technically, the average of each loan is the interest paid / the interest rate; then add the results together for the two mortgages to get the average balance for the year..
see publication 936, page 13 in the middle column
https://www.irs.gov/pub/irs-pdf/p936.pdf
your result should be about what you are expecting, regardless of what TT says
