If you connect 2 tanks with a decanting hose, they will equalize but after that they won't mix if you'd leave them connected and opened (I wonder how many weeks it would take to have an equal mix this way).
Best way for this approach is probably to decant each tank into an empty buffer tank, which requires a booster (and lots of drive gas!), preferrably a 2-step booster if you want to empty each tank into the buffer. The end mix that this would produce can be calculated when you take the pressure and analysis of each AL80 - calculate the volume of each gas, add it all up and that's the theoretical end mix. Filling the divetanks would require the booster again. Temperature differences caused by decanting and boosting will influence the analysis.
I guess this time consuming and labor intensive process doesn't sound appealing. Another approach is determine the mix you want to dive with, decant from the AL80 straight into the dive tanks and top up the required gasses to achieve the desired end mix. Also time consuming and might require a booster as well.
So...not easy. Mixing from a helium and oxygen buffer is much easier.