Build Recurring Income

I am going to be receiving ongoing income from my grandfathers estate. I have been told that it is taxable because it is classified as income not an inheritance since it is income earned by the estate since his death. I an trying to get an idea of what tax rate I should expect to pay. I do not know yet exactly how much I will be receiving.

My wife filed a return of income with taxable income below taxation limits. Source of income tutions and rental. Tution income was received in cash. ITO says the onus is on her to prove that her income was not more than what was reported. How does one do this?