わけではない vs わけがない vs わけにはいかない

It's not that/Not necessarily

It does not mean that ~; I don't mean that ~; it is not that ~; it is not true that ~; it is not the case that | A phrase which is used to deny what is implied in the previous or following statement.

1. A：この病人は全く助からないんですか。B：いや、そういうわけではありません。

   A: Can this patient not be saved at all? B: No, it is not that he can't be saved.

2. あの人が嫌いだというわけではないんですが、結婚したいとは思いません。

   I don't mean that I don't like him, but I do not want to marry him.

There's no way/Can't be

There is no reason why ~; it is impossible (for ~) to ~; cannot | A phrase which negates the existence of a reason to believe that someone does something or is in some state, or that something takes place; or which negates a possibility of someone's doing something or being in some state, or something's taking place.

1. あの店の物がこんなに安いわけがない。

   Things at that shop cannot be this cheap.

2. こんな易しい仕事が君に出来ないわけがない。

   There is no reason why you cannot do such an easy job.

Cannot/Must not

Cannot; cannot but ~; cannot help -ing; have no (other) choice but to ~ | A phrase which is used to indicate that one cannot do something due to an external circumstance.

1. この論文は重要だから、読まないわけにはいかない。

   This paper is important, so I have no choice but to read it.

2. これから運転しなければなりませんから、酒を飲むわけにはいきません。

   I have to drive from now, so I cannot drink.