What´s the difference between なってきています and なっています?
For example: お隣の人達、大丈夫? ヤバくなってきているよ。
Would it´s meaning change significantly if it´s changed into: お隣の人達、大丈夫? ヤバくなっているよ。
It would be helpful if gave specific examples because what seems like a simple question touches some quite complicated grammar, which I will try to cover briefly:
First you need to understand the nature of ~ている. There are several questions covering this quite well so I won't repeat them but will try to summarise:
なる is a "punctual verb", that is to say that when using the ~ている form, the resultative state precludes the continuative state. In other words if we say:
This usually means:
It can also mean "is becoming convenient" but to convey that sense (ie it is in a transition state) additional words, typically adverbs are often used to create the context. eg:
Second: 〜てくる／〜ていくis used to convey change in position or time. Often these communicate the movement/action of the speaker (「いってきます！」）or movement of something/action with respect to the speaker (「電話がかかってきた」）but they can also be used to convey continuation of a state or "process of change". eg:
For example, 暖かくなってきています is "it's getting warm" while 暖かくなっています is "it has become warm" = "it is warm".