You made of money man? Ha ha 3 high-end cameras would be after winning the lottery for me.
You only need 1 or 2 of them.
Either the high-res/low ISO and low-res/high ISO combination, or the general-purpose one. Or just one of them (or two of the same one) if what you shoot is more restricted.
It's no different to the 1D3/5D2 combination that used to be popular, or the D810/D4s combination.