Since all the children of your father i.e., yourself, your brother and sisters are adult and have married and settled down, nobody can claim maintenance from your father. I presume all the properties standing in the name of your father are his self acquired properties including the FDs. Given the situation, neither you all nor your mother can legally claim any share in the immovable or movable property of your father as legitimate right.
Your mother can claim residential rights, but since she has been allotted with the house in which she is residing now, she is not entitled to further rights in his property. She can claim monthly maintenance under section 125 Cr.P.C.. She can lodge a complaint against your father for the offences of bigamy. She can file a suit to declare your father's marriage with that lady as null and void on the grounds that his earlier marriage subsists and he has a spouse living from his previous marriage.
Thus, any claim that can be made shall be made only by your mother that too on the above lines alone, especially during the life time of your father. He cannot be restricted from disposing his self acquired property in the manner he desires to and to the person he chooses.