Check if two family members are siblings.
        
        Arguments: 
            individual_1_id (str): The id of an individual
            individual_2_id (str): The id of an individual
        
        Returns: 
            bool : True if the individuals are siblings
                   False if they are not siblings

def check_siblings(self, individual_1_id, individual_2_id):
        """
        Check if two family members are siblings.
        
        Arguments: 
            individual_1_id (str): The id of an individual
            individual_2_id (str): The id of an individual
        
        Returns: 
            bool : True if the individuals are siblings
                   False if they are not siblings
        """
        
        self.logger.debug("Checking if {0} and {1} are siblings".format(
            individual_1_id, individual_2_id
        ))
        ind_1 = self.individuals[individual_1_id]
        ind_2 = self.individuals[individual_2_id]
        if ((ind_1.father != '0' and ind_1.father == ind_2.father) or 
            (ind_1.mother != '0' and ind_1.mother == ind_2.mother)):
            return True
        else:
            return False