Bought a property where minors involved

Sir/Madam myself Laxmidevi. I m living in Vijayawada, AP. I bought a plot in 2004 from a woman. Her husband died in accident in 2003 and by virtue of law she got that property. At the time.e of sale, it was mentioned that as a guardian of the two minor children the wife of the deceased plot owner took all responsibilities pertaining to the property and solmonely declared there won't be any sort of legal problems from her or her relatives etc. She also gave a slef affidavit signed in front of SPL executive magistrate where she declared that her two children and herself are the only legal heirs of the deceased person and if anybody proved her statement wrong she would take responsibility. This affidavit was given to us at that time. Now after 12 years, I want to construct a house in that plot by taking bank loan from SBI. They sent all the related documents of that plot and telling that a family member certificate is needed asminors are involved in that property. We told them about the affidavit but they are not accepting that and telling FMC is must or we have to wait for 30 years. What should we do now. The family of that woman is not here and we dont know where they live. Pl help.