I am a new Muslim and I have a mortgage over 25 years.. this debt was incurred before converting to Islam.. I have no means to pay back this loan as it is a large sum and it provides the home in which my children and I live...
Are there any conditions in which someone can pay back a loan with interests?

You are to repay the loan at its due date according to your agreement with the bank. It is not obligatory upon you to repay it all at one time.