Help! Which one is the true sentence?

Both grew up and have grown up are active voice. Grew is the straight past tense of grow. It is an action that was performed by your parents at some time in the past.

Have grown up is the present perfect tense of grow and it indicates a more recent past action, but it is also active voice.

If your parents were still living on the island than it would be ok to use this tense.

Because they no longer live there, b is correct like everyone else says.

I have a question for you. Is the island no longer there because you say it "was" a small island.

b) is the correct sentence.

It's hard to explain why the first sentence doesn't work, but I'll try! In English we might say "My children have grown up and moved out of the house". But we would say "My children grew up in England". The first one implies a maturing whereas the second just refers to childhood as a whole.

b, because if you and your parents still live there, they have grown up there, but if you leave, that is where you grew up. also, have grown up is passive voice, which you should try to avoid in all cases.

personally i think "where my parents have grown up" just sounds kinda awkward

b is correct.

the fear of a tsunami was so strong, they decided to move.