Yes, you can eat and use whatever he earns as the sin is only on him.

I am disabled and bedridden patient so i am dependent on my father financially who is retired govt employ. His major income is his pension which is used to run the house. But he has also invested some money in National Saving Scheme which most scholars say is riba based. It makes about less than 1 third of his total income. So can i eat and use money given by my father?