You just don't fit the income criteria now with your financial situation and dependents. Take the longer term and just pay whatever the repayments would be on the shorter term and it will finish as normal within the shorter term, basically overpaying. Assuming that is you can overpay on that rate, is it fixed?
The only disadvantage to this option is you will have to have mortgage protection for the new term chosen but for most people with standard underwriting that won't be a big extra cost.