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

Yes

The word "estiveram" is identical in meaning, spelling, and grammatical function in both Brazilian and Continental Portuguese. It is the third-person plural of the verb estar in the Pretérito Perfeito do Indicativo (past tense). The only difference is in pronunciation. In Brazilian Portuguese, the vowels are generally more open and clearly articulated. In Continental Portuguese, unstressed vowels often undergo reduction, meaning the "e" might sound much more closed or nearly disappear, and the overall rhythm of the word is more staccato.

Brazilian Portuguese Examples

1. Eles estiveram no shopping ontem. (They were at the mall yesterday.)
2. As crianças estiveram muito quietas hoje. (The children have been very quiet today.)
3. Meus amigos estiveram na minha festa. (My friends were at my party.)
4. Eles estiveram estudando muito para a prova. (They have been studying a lot for the exam.)
5. Os alunos estiveram ausentes na aula passada. (The students were absent in the last class.)

Continental Portuguese Examples

1. Eles estiveram no centro comercial ontem. (They were at the shopping center yesterday.)
2. Os miúdos estiveram muito quietos hoje. (The kids have been very quiet today.)
3. Os meus amigos estiveram na minha festa. (My friends were at my party.)
4. Eles estiveram a estudar muito para o exame. (They have been studying a lot for the exam.)
5. Os alunos estiveram ausentes na última aula. (The students were absent in the last class.)