The simple answer to this question is YES you can take a loan out on the property if its is under a lease agreement as long as you are on the title of the property. However, the underwriting guidelines will be more difficult to qualify due to the fact it has to be considered a rental property from an underwriting standpoint & the mortgagees will have to be able to qualify with regards to income, credit, and loan to value ratios.
Have you looked at the options for your mother to take out a reverse mortgage on the property to cover her living expenses? This would eliminate you from having additional payments and having to qualify with regards to income and credit. In addition, if the individuals buys the home in the future you would just have to payoff the balance of the reverse mortgage prior to the title being transferred to the new owners.