Is it permissible to donate a portion of the insurance money received by the heirs due to the death of their father in an accident, and what is the specified percentage for that?

If the father died due to an error, and the at-fault party or its 'asabah (agnates/clan) referred you to an insurance company to collect the blood money (diyyah), there is no sin in that. You are not obligated to donate any part of what the insurance company paid as charity. However, if the heirs agree to donate a portion of the compensation as charity on behalf of the deceased, there is no sin.