+1 on this advice.Run them separately. But cross the inflow and outflow:
The inflow of filter1 sucks water from the left. The outflow of filter 1 discharges the water in the right side of the tank.
The inflow of filter2 sucks water from the right. The outflow of filter 1 discharges the water in the left side of the tank.
I have two Eheims on my fairly heavily planted 72 gal (see "My Tank" link in my signature). I am running them independently. A 2026 with an inline PVC CO2 reactor on the outflow and a 2028. Only difference to above is I have the 2026 output spray bar across the middle of the back with three holes in the output spray bar pointing across the top middle (back to front) of the tank, three holes pointed down against the back glass, and I drilled one hole in the elbow to spray to the left (facing tank left), this way to disperse the CO2 enriched water about better in three directions. The output spray bar of the 2028 is on the left side spraying mostly across the tank left to right (and mixing the main 3-hole output from the 2026 CO2 outflow water) and one 3-hole section pointing down. I also have a Koralia 2 on the left side, sort of towards the back, pointed to the right front corner. Until I did all this I was getting patches of BBA from time to time even though my CO2 drop checkers were a nice lime green. Since being over-the-top in my efforts for large dispersement the BBA has dropped off for just the occasional tuft here or there (easily treated with H202 or Excel) and I attribute this to better CO2 dispersement around the tank.
I was just given a used but working XP3 and plan to add that too since I am fairly heavy on the fish load and I really do not see how "over-filtering" would be an issue. Some people recommend in filtering to go 10x the manufacturer's rated pump output vs. your tank's gallon size (not flow).
I'd consider at least one of your Rena's be an XP3 if not both. It will not hurt.