Zusatzstoffe zu VW Tiguan CUBE und VW Jetta BXE

Hello, I drive 2 cars VW Tiguan CUBE (120,000 km) and VW Jetta BXE (290,000 km)

I was very confused about which oil and fuel additives to use. There are 3 different engine cleaning additives: Motor Clean, OIL SLUDGE, ENGINE FLUSH PLUS. Can you tell me which one to use What's the difference between them?

Second, there are 4 different oil additives: Cera Tec, MOTOR PROTECT, OIL ADDITIVE, LIFTER ADDITIVE

Can you please tell me what and when to use it?