can i put jet-a in my vw?

I am not an automotive engineer, and can't tell you what the long-term effects would be to your engine, but I can tell you that when we drained fuel from an airplane's fuel tank and we couldn't put it back in because it was legally "contaminated", we used that contaminated jet fuel in our diesel pickup and ground equipment with no serious problems.

Some people recommend adding a liter of engine oil to several gallons of jet fuel because jet fuel does not have the same lubricating qualities as diesel, and the diesel engine's fuel injectors and fuel pump need some lubrication.

Most airlines have a lot of diesel powered ground equipment. It all runs just fine on Jet-A. There is some minor degradation of fuel system components, such as injector pumps due to the lack of lubrication in Jet-A.

You could, but it won't give you any extra performance. I also wouldn't recommend it - there's apparently less lubricating properties in Jet-A than regular diesel and in an automotive TD engine it might cause some problems. However, that's a question for a qualified VW tech in the automotive forum to answer.

Diesel has a lot of oil left in it, Jet A does not. The fuel pump uses the oil in the diesel for lubrication, and with Jet A may seize and quit working.

In theory it can, but it would not run well without being configured to use it.

no, this is not family guy and it would most likely destroy the engine