Re: Isn’t the air density and gravity different
"Perhaps they should use Apollo era parachutes, they all folded into an impossibly tight space yet never failed and they didn't have long to test them."
The Apollo parachute system was designed after about two decades of US experience - beginning in WWII - in dropping heavy loads retarded by multiple parachutes so that even if some parachutes failed, the load would survive. It was handy for air-dropping trucks and the like.
One Apollo mission did suffer a parachute failure, as you can see here:
The Apollo system was worked out so that a two-chute splashdown wouldn't harm the astronauts or split the command module open. It was a hard bump when Apollo 15 hit the water, but not a big problem.
The thing about the ExoMars mission is that they're trying to get it to work without redundant parachutes - well, you would, wouldn't you?
As for the differences between Earth and Mars atmospheres and gravity and so on: I'd guess that they've done some number-crunching to work out what combination of Earthly release altitude and subsequent parachute opening altitude corresponds to an aerodynamic loading on the parachute system similar to that which will be experienced when entering Mars's far thinner atmosphere at far higher speeds.