Need advice on really weird situation....please

i have a weird situation. over 5 years ago we sold our house in new jersey and moved to florida. somehow our second mortgage through gmac did not get paid off. didn't notice it at the time because we didn't go to closing. it was a mail away. we had been living in fl for about 8 months by that time and had totally divorced ourselves from the situation. anyway, we got the first bill and thought it was nothing. next bill came and we pulled out the closing papers and realized then that it had never been paid off. by then we didn't have the full amount to pay them so we continued to pay the monthly bills figuring sooner or later we would be able to pay them back. so for 5 years i have been paying a mortgage on a property i don't own. no biggie, i owed it so i kept paying it. well now we are really having a hard time paying our mortgages and that one is the worst because the interest rate is over 10% now. i'm not sure what to do. i know i owe it and i don't want to get out of paying it. that's not my question. i can not refinance any of our mortgages because we don't have any equity left since the atrocious downturn in housing. we have a mortgage on our home and also a mortgage on a home my oldest daughter lives in. she has recently come down with lupus and needs all the help we can give her so we can not sell that property, at least not yet. my husband and i had jobs having to do with the housing market so our income has been reduced by 90%, so we couldn't refinance even if we had equity.

if i notify gmac that we can not continue to pay that mortgage at the rate that it is at, do you think they will refinance to a lower rate or will some crazy bell go off and they will want all the money at once at ruin our credit. the one thing we have left is our great credit. is their anything criminal in what we did? can we get in trouble in any way? i'm so afraid to bring it to their attention but it is going to bury us soon and i don't want to go into default on our bills. any help is greatly appreciated!!!! sorry about the long post.