Can I have all 3 of my children be executor of my estate?

You can name as many executors as you want, or can name a primary executor and secondary ones to act if the primary does not or can not do so. But if you name all three, unless they are extraordinary, it will be very difficult to get all three to agree to any single course of action involving any significant amount of money or asset. It is best that in your Will, you state as much as you can as to how you want the assets you have at death divided up [giving any one asset to more than one child will create problems]. There is almost a 100% guarantee that the nicest child will be taken advantage of by their siblings.

This is a bad idea that will result in confusion. Name them in successive order.