Why the surge brakes on the second trailer?
I double with about the same set up you are planning and I have elect brakes with no problem, I just have a second brake controller in the truck to run the second trailer, I have never seen it sway or buck( I have 2 cameras on the back of the 5th to keep an eye on things)I guess if it did sway i could always tap the second trailer brakes to get things settled down. anyway i don't think you will need the weight dist hitch with that light tongue weight
what ever you do good luck and be safe
Kevin