Some thoughts from someone who actually drove on the ring, not only in GT5:
a) 4 people in the car is no issue. But you have to adjust your speed. If you don't: stupid
b) not wearing a helmet: toll road, no helmet required. Should you consider wearing one? For sure if you drive a car with a rollcage. For sure if you drive a car without side and window airbags. Not so sure if you drive a car with full airbags because it could be counterproductive taking into consideration the additional weight above your neck.
c) Wippermann is a tricky part of the track but not too difficult. You have to let the car roll through it rather than unsettling it by braking and accelerating. In the wet, any part of the track is super slippery, so: adjust speed and your racing line
d) Lowering springs and standard bumpstops might not be the best scenario combined with a fully loaded car and a bumpy track.
e) since the question came up: Pflanzgarten 1 is not too tricky. Got to get your braking right. The bend itself has a lot of grip. Pflanzgarten 2 is the corner with most drop on the whole circuit. So you better have the car straight going into it. Not too difficult.
Pflanzgarten 3 is the trickiest of them because you are already very fast (100 mph in an M3, I estimate). It is blind. Has a big bump in the middle. Especially RWD cars can lose traction here as you usually take it flat-out.
f) since the car has a brembo BBK I will make a wild guess now: the driver found out that the stock brakes might have a heat problem. The heat problem can be cured by using fresh fluid (as you always should when going to a track) and other pads and most importantly: adjust your driving style to the vehicle. So, by putting a BBK in it, the driver can mask his inability to adjust the driving style to the car. And the reaction or lack thereof shows that the driver might not be the most experienced.
I never understood really why people throw tons of $/€ at a car instead of learning to f*ing drive it properly. For the money the BBK costs the driver could have participated in a number of very good driver trainings.