Enter into????... it should be revised, should'n it?
"To enter" already has the meaning of "going into", so "enter into" is redundant.
"We don't need to enter the castle." Why is this incorrect?
"precisaremos" is the future tense. You need to put "we won't/will not," not "don't/do not."
This is plural tense: nós não precisamos entrar no castelo.
We shall not need to enter the castle.