I hope I didn't confuse you earlier; your bankruptcy attorney is likely to be perfectly competent if he was able to get your Chapter 13 Plan confirmed (trust me, it's not easy!). I was thinking about ways to lower your monthly payments but didn't really address your questions and concerns as clearly as I should have. Here's a better explanation addressing the issues I believe you were actually asking about:
When you include the mortgage in your Chapter 13 Plan, the bankruptcy court has the power to judicially rewrite the terms of your mortgage contract. This means that the provisions in your confirmed Chapter 13 Plan override the contractual provisions in the mortgage.
I'm guessing that what the bank was trying to tell you last year (although it probably wasn't articulated very clearly) is that the first mortgage (only) would be paid off in five years if you continued making timely payments in the full contractual amount each month.
Now I'm guessing that the bank has subsequently combined the principal balances and arrears on the two mortgages and lowered your effective monthly payment. However, as a result of lowering your effective monthly mortgage payment, the loan was probably re-amortized so that it will now take 12 years to pay off.
Also keep in mind that the monthly payments you're sending to the bankruptcy trustee include not only your mortgage payments, but also your car payments, small dividends for your unsecured creditors (credit cards, personal loans, etc.), attorney's fees for your attorney, delinquent taxes (if applicable), and a trustee's fee of about 10%.
Thus, your mortgage will likely NOT mature in 2018 (unless the Plan provides for it to do so), and you probably don't need to worry about having to make a potential balloon payment or anything of that nature so long as you continue making your regular monthly mortgage payments after your Plan ends. You should really check with your attorney on this issue though, as your particular case could differ; I have, for instance, seen Plans that provide for a huge balloon payment in month 60.
If you decide that the mortgage payments are simply too expensive and you want to walk away from the home, you are allowed to do so while you're still in your Chapter 13 Plan, but the catch is that the bank would then be allowed to foreclose on your home while you're still in your Chapter 13 Plan as well. Again, you should speak with your bankruptcy attorney about this if you're considering it as an option, as there could be serious financial consequences if this isn't done correctly.