"So since my wife does not work would it benefit us to put 2 dependents (for our two children) on the w-4?"
It depends on what you mean by "benefit." Adding dependents on your W-4 will reduce the amount of tax that is withheld from your pay, so your take-home pay will increase. The reduced withholding will mean you get a smaller refund when you file your tax return. To see what the effect would be of changing the number of dependents you can use the Tax Withholding Estimator on the IRS web site or the TurboTax W-4 Calculator.
"what is 'Your total tax for the year' ?"
For the purpose of this discussion, your total tax for the year is the amount on Form 1040 line 24.
