I received an Intent to Accelarate Notice

Hi my name is Evelyn my question is my father lost his job 2 yrs ago however he has two loans that they call 80/20, but continued to give the mortgage payments he modified our home and included property taxes in the mortgage payment. He then went through a second modification to lower the mortgage payment more because the property value went down. He was denied of it and started to submit documents directly through B of A. He received noticed of intent to accelerate but he never stopped giving them payments. Payments he's made have been going to the principal loan which is the 80% loan and has stopped paying the other 20% could they foreclosure our home even dough he is making partial payments? The letter indicates that he owes since back in April 2010 and when we calculate the amount that they say its due it comes out to the whole mortgage payment. We where advised that we could do a short sale but we don't really know how that works. At this point we are worried we might loose our house due to the fact of my dad not paying the small loan. My father did these modifications through a broker and she advised him that short sale would be the best option now. During a modification process/ or a short sale do we still continue to give payments or do we stop. Please advice any helpful information someone could please give as I dont want to keep paying for something eventually I am going to loose.

Kind regards,

Evelyn Montano