Based on what you've noted, I read that Mortgage #1 & #2 were paid off with Mortgage #3. If this is in fact true and correct, both M1 & M2 have a remaining balance of Zero ($0.00) at the end of 2019. For Mortgage 3, if you made any payments in 2019, the remaining balance should be less than the original amount financed. The 'remaining balance' for 2019 should be at the bottom of your 1098 for Mortgage #3. At least that's where it is on mine. (remaining balance is the 'principal remaining balance'.
Best
