Is the word preferem the same in Brazilian and European Portuguese?

Yes

The only difference between "preferem" in Brazilian Portuguese and Continental Portuguese is pronunciation.

In Brazilian Portuguese, the vowels are generally more open and the syllables are articulated more clearly. The "e" in the middle of the word is pronounced distinctly, and the nasal "em" at the end is clearly voiced.

In Continental Portuguese, the vowels tend to be more "reduced" or closed. The unstressed "e" is often shortened or nearly swallowed, making the word sound much more compressed (approximating a sound like pref'rem).

Brazilian Portuguese Examples:

1. Eles preferem comer pizza no jantar. (They prefer to eat pizza for dinner.)
2. As crianças preferem brincar no jardim. (The children prefer to play in the garden.)
3. Meus pais preferem viajar de avião. (My parents prefer to travel by plane.)
4. Vocês preferem café ou chá? (Do you [plural] prefer coffee or tea?)
5. Os alunos preferem estudar na biblioteca. (The students prefer to study in the library.)

Continental Portuguese Examples:

1. Eles preferem comer pizza ao jantar. (They prefer to eat pizza for dinner.)
2. Os miúdos preferem brincar no jardim. (The kids prefer to play in the garden.)
3. Os meus pais preferem viajar de avião. (My parents prefer to travel by plane.)
4. Vocês preferem café ou chá? (Do you [plural] prefer coffee or tea?)
5. Os alunos preferem estudar na biblioteca. (The students prefer to study in the library.)