NASA is putting pause on sending commands to its Mars exploration instruments from November 11 through November 25 as it waits out the Mars solar conjunction. With the sun in the way, any commands sent to Mars could suffer interference capable of harming the robotic explorers.
Did you mean L5? L3 is always in line with the sun, so it doesn’t seem like it would be useful for communication.
Would it be easier to have a separate satellite for each direction, one at the Earth-Sun L4 point, and one at the Mars-Sun L4 point? Could we get a large enough dish to the Earth-Sun L4 point?
Alternatively, could we use lasers instead of radio? The SpaceX Starlink satellites have laser inter-links, and NASA just sent up the ILLUMA-T payload to the ISS last week.