I will not touch the triple tow thing...too many laws and license questions.
There are 3 basic types, pivot pan (toad wheels on a pan that pivots), steering axle (toad wheels are on a fixed frame and the dolly's wheels turn like a car, and fixed tray (simplest type, car's front steering lock remains unlocked and the toad's front wheels pivot just like flat towing).
All 3 types can have brakes. There are surge brakes (fully automatic self contained adjusting hydraulic) and electric (requires a brake controller in the towing vehicle - just like the 5er).
These brakes can be disc or drum style.
I have a fixed tray dolly with surge disc brakes. It is the best in my opinion.
Dolly towing is smart to protect the car with less risk of rock strikes, no baseplate mount in the bumper or crumple zone, and no miles on the lower driveline like with flat towing.
There are many many dolly makers for your selection.
Kim and Steve, Mustang LCDR (Ret), '07 Damon Outlaw #1193
I have seen gross intolerance shown in support of tolerance, Samuel Coleridge
WE LOVE OUR OUTLAW RV