You can give 15k per person per year (may have gone up in the past year) without reporting it. Anything more than that you have to report it, and it counts against the untaxed portion of your estate. Aside from that 15k per person per year value, there's no tax difference between giving it away now, or willing it away when you die.
Estate and gift tax are intertwined. There's even a page on the IRS web called "Filing Estate and Gift Tax Returns".
https://www.irs.gov/businesses/small-businesses-self-employe...
It might be easier to work things out while you're alive to make the gifts, but it doesn't get you out of the taxes.
You're correct that if they gave all 1.2 million in one year, it's subject to tax, but no one does that.