Breakdown of O teu irmão é que precisa do martelo e da ferramenta.
e
and
o irmão
the brother
teu
your (informal, m/f/pl: teu, tua, teus, tuas)
precisar de
to need
Questions & Answers about O teu irmão é que precisa do martelo e da ferramenta.
Why use "é que" here instead of just saying "O teu irmão precisa"?
Adding é que puts a strong emphasis on the phrase right before it. While O teu irmão precisa simply means "Your brother needs", inserting é que changes the focus to "It is your brother who needs". It highlights exactly who needs the tools, perhaps correcting someone who thought you needed them instead.
Does "é que" change its form if we were talking about multiple brothers?
No, and that is the beauty of this emphatic structure! When used for emphasis in a declarative sentence, é que acts as a fixed, unchanging particle. Even if the subject is plural, like Os teus irmãos é que precisam, the phrase é que stays exactly the same. You only conjugate the main verb (precisam) to match the subject.
Why is it "do martelo" and not just "o martelo"?
The verb precisar (to need) is almost always followed by the preposition de. When de bumps into the definite article o (the) right before martelo (hammer), they combine into the contraction do.
Why is there a "da" before "ferramenta"? Couldn't we just say "do martelo e a ferramenta"?