Property

You said the flat is in your mother's name.   But your father purchased the flat.  Then how is it in your mother's name?  who is paying Municipal tax?  Is your housing society  transfer your mother name?

Details are inadequate as there is no mention of Father's claim on the property, who is at present enjoying the property, at whose instance the repairs were done, who is enjoying the property etc.   Contact a local advocate for exploring possibilities if any (though remote).

If the father had bought the flat, how is it in mother's name? Had she any source of income?

If the flat is inherited by your mother you have a share with your mother and other siblings in it left intestate by your father

Presumption and assumption may lead to form an inappropriate opinion, hence post all facts otherwise, consult a local prudent lawyer for proper appreciation of facts/ documents, professional guidance and necessary proceedings.

Expenditure incurred for interiors of the flat can not be claimed/ recovered.