Despite Rand al'Thor already having posted a very nice answer, I thought I might provide some super high quality MSPaint diagrams, as well as an alternative method.
(Hints are dropped throughout the answer in the form of which clues to use first)
On each floor there are three bedrooms: one on the left, one in the center and one on the right.
First we'll deal with these two clues:
- Janice lives directly above Lucas and directly beside Marta, who lives on the left.
- Eduardo lives on the right and one floor higher than Janice.
Janice must live on the 2nd floor or above, since on the first floor she would be above no-one. This means Eduardo must live on the top floor, on the right.
This in turn means that Janice must live on the 2nd floor, which means Marta must be on the second floor as well (to the left).
Next we will deal with this clue:
- Camila lives directly above Janice.
Camila must live on the 3rd floor, since she is above Janice, who is on the 2nd floor.
Camila cannot live where Eduardo is, nor can she live on the left, otherwise she would be above Marta and not Janice. Therefore Camila and Janice live on the centre rooms, in their respective floors.
Additionally, Lucas lives underneath Janice, which means he must live on the centre bottom room.
Now we can deal with this:
- On no floor only girls live.
Very simple given our diagram - we see that the second floor has 1 empty space and no boys! Therefore Mateus (our only remaining boy) must go there.
At this point we can stop, since we already have the answer:
Marta, Janice, and Mateus (left, centre, and right respectively)
However we can finish the puzzle, using our last clue, so why stop there?
- Giulia lives directly above Cristiane.
Since there are only 2 remaining spaces which are vertically over each other, we know Giulia and Cristiane must go there, with Giulia at the top floor and Cristiane on the bottom floor.
This leaves only one last space for Alessandra!