To see what the IRS recommends, you would fill out the worksheets on both sides of the W-4 form (for two jobs, and taking into account your deductions and dependents). That gives you a number of allowances you can claim. You don't each claim them -- you divide them between you. So if you have 4 allowances on the worksheet, you might give your employers new W-4 forms that claim 2 each, or one person 4 and one person zero. If you want a larger refund, claim fewer allowances (you will see a dip in your take home pay of course).
For an accurate estimate now (based on not changing anything) use this calculator. It requires detailed input but will give a detailed and correct answer. https://www.irs.gov/individuals/irs-withholding-calculator
You can also use the calculator if you change your withholding, after you get the first couple of paychecks with the new withholding.
I also agree that if you simply leave things alone, you will probably get the same or a larger refund. Your W-4 does not have to match your lifestyle (# of dependents, married, etc.). It is just a tool for determining your tax withholding and does not have to match your tax return.
