Hello,
the brake pads wear sensors do not do anything to the ESP, they only signal a brake service warning on the dashboard. The ESP/cruise error etc. can be a lot of things - e.g. brake pedal switch can cause this, a jammed ABS controller (not passing self test) can cause this. Every error code can be read from a good tool like SDS, autologic, maxidas etc. etc.
The service indicator can be reset if you want - your freinds car sounds like a classic Pakistani benz owner who drives it into the ground because (mercedes mazboot gaddi hai) - no offense intended.
Filters are available everyday, the brands are MANN, Hengst, Bosch and Genuine Mercedes Benz. Brake pads OE are either made by Textar or ATE depending on the car build sheet.
Just like the ESP the engine check light can be scanned to see whats up - I would suggest you find a sensible person to give you a scan log for your car and then proceed to get it back into good shape.
I hope the ABS module is not jammed due to missing brake fluid flushes.