you were not on the original debt so you did not refinance the debt. if you did not refinance the debt it can't be acquisition debt. if it is not acquisition debt then you can't deduct the interest. there is an exception to this if you are an equitable owner (not on the title). an equitable owner is a person who has the economic benefits and burdens of ownership, based on the facts. occupying and maintaining the home and paying the mortgage and taxes on it are factors that might indicate equitable ownership.
when it comes to refinancing there can be limits on the portion of the interest that is deductible regardless of whether you are an actual or equitable owner.
you could not have purchased the home because you apparently are not on the title to it.
