Sometimes we need the preverb in these sentences, sometimes we don't. I wish they'd just decide whether to include them or not and stick with it, because right now it's a real 50/50 crapshoot as to whether or not your answer will be accepted.

The right translation should be: I am going to sit in the car ... because I sit into the car' sounds really weird in English

is "be" necessary?

I am getting into the car ' is also correct

Confusion here: is the guy getting into the car to drive away, or is he just going into the car to have a quiet place to sit for a while? I'm frustrated by added precision in Hungarian adding to confusion in my working to depict what is happening. I guess context would help.

the "abba" and the "be" together is redundancia

Does this mean that I am sitting in the car, or that I am getting in the car? Either way, you can't sit into a car in English. Because of "be" in the Hungarian I think that it means the latter, but that's not the way you say it in English. I appreciate that there are many differences in this area in the way the two languages express the same ideas, but I wonder if the course designers could have chosen sentences where the differences of idiom are less of a problem for learners. Maybe that would not be possible. Was it considered?