How do we add ownership interest!

My mother made a substantial down payment (1/3 total value) for a home for my husband and me in 2008. My mother does not live in the home and it is the primary home for my husband and me. Because my mother made such a significant down payment on the home, the home is in her name. My husband and I pay her monthly rent equal to the mortgage payment and we pay for homeowner's insurance and all home repairs and upkeep. At this point, we would like to set up a 'joint tenancy with survivorship' with all 3 of our names. Because the home is still mortgage, our attorney advised us that the lender would need to my and my husband's name to the title/mortgage interest. When the lender refused to do this, we attempted to do a refi to accomplish this. Even though we all have good to excellent credit, we can't find a lender to do the refi simply because this isn't my mother's primary home. Any advice?