Hi - the parking system should be checked on a diagnostic tool such as Mercedes STAR diagnosis - any faulty sensors will be stored as fault codes in this system and this will pinpoint the exact sensor(s) at fault so they can be replaced
With regards to the TV - Mercedes has no solution for converting an analogue system to a digital one I'm afraid. There are however some aftermarket solutions out there but they are very expensive (any thing up to £1000 depending on the exact system needed) last time I checked. I would recommend speaking to a local car audio specialist as prices change quite frequently for products like this.
I had looked into this with a specialist that we use for aftermarket installs but the customers I spoke to all thought it was too expensive (as do I!)
Let me know if you need anything else
Best regards, Paul