I made 120k and my wife made 60k. Together we are over the 160k phaseout for the third stimulus check. We also have 2 children. So, that would be another 2,800 that we are missing out on. Should we fi

Nothing is final as of this writing, however based on what we know- 

Thus far, the payments are based on the same requirements as the first two checks: The full amount will go to individuals with up to $75,000 in adjusted gross income and married couples filing jointly with up to $150,000 in income. In addition, children and adult dependents may also be eligible for a $1,400 check.  This may change.

In the past the phase out has been based on your AGI, not total income.  

If they base the qualification on  your most current AGI and you have not filed for this year it may be an advantage to wait.  This would be a personal decision. 

Hopefully, we have a decision from the government before the required filling date.