We are looking to buy a new car. We will only buy Toyota of course they are the best cars and most reliable. We will be having our fifth baby in July and need a bigger car. Which ones best a sienna or sequoia?

I'm guessing you've made your decision already, but here are my two cents:
the Sienna will be very easy to drive, put kids in and out, with tons of space for groceries.
The new Sequoia is gigantic, it is much more difficult to drive, much taller with less storage space for daily groceries.
you would only get the Sequoia if you need offroad capabilities. It also gets only 12 miles per gallon!