Slice the bananas and place in a cooking pan with water. Cut the lemons in half, squeeze out the juice and add it to pan. Slice the lemon rind and pith, tie it loosely in a muslin bag and add it to the pan. Add the sugar, bring to a boil, stirring. Then simmer 1 to 2 minutes. Cover the pan with a clean tea towel and let set overnight. Next day, bring to a boil again and boil the jam rapidly until setting point is reached. Remove the muslin bar. Pour the hot jam into hot clean jars and seal.