Praise be to Allah.
It should be noted that this taxi which your father registered in the name of his youngest son -- because of insurance reasons and so on, and it was not a gift and was not meant to become his property -- is regarded as part of the inheritance in which all the heirs have a share according to the shar’i system of division.
You have to get rid of the interest/riba by spending it in the public interest or on charitable causes. It is not permissible to get rid of it by benefiting from it yourselves, unless you are poor and in need. In that case it is permissible to take from it according to need, as stated by some scholars with regard to haraam money after repenting and giving up the sin. Please see the answer to question number 126045.
It is permissible for the one who is getting rid of it to give it to his poor brothers from whom he would not inherit in the event of their death, or he may give it to them to pay off their debts. For more information on that please see the answer to question number 81952.
If it was decided that this taxi was the property of all the heirs and its price was put in the riba-based bank, then this interest belongs to all the heirs, and each of them may get rid of his share by giving it to his brothers from whom he will not inherit.
If those who are in need take their share of the interest and spend it on themselves for education and the like because they are poor and in need, that is permissible as stated above.
And Allaah knows best.