I see a lot of posts where TT struggles to calculate interest when there are multiple 1098's involved and folks struggle to understand 'average loan balance'.
"average loan balance" is determined by
1) taking the interest for the year on a specific mortgage and dividing by its interest rate. THAT is its average.
2) sum up each average (you have three of them) and THAT is your average for the year.
You don't simple take a two point average of the three mortgages which is going to overinflate the average mortgage which reduces the deductible interest
see publication 536 page 13 and read the middle column
https://www.irs.gov/pub/irs-pdf/p936.pdf
