Two LEGO Powered Up engines with reverse direction
Th easiest solution is to just use port "B" on the rear engine and then turn the "B" side remote control panel 180 degrees.  They will then both go the same direction for "up" or "down". You may even find that having the rear motor 1 click lower than the front is advantageous so it isn't pushing too much in turns, trying to buckle the train.