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

Yes

The word "nestes" is a contraction of the preposition em (in/on/at) and the masculine plural demonstrative pronoun estes (these). There are no differences in meaning, grammar, spelling, or fundamental usage between Brazilian and Continental Portuguese. The only difference is phonetic: Brazilian Portuguese tends to pronounce the vowels more openly and clearly, whereas Continental Portuguese frequently reduces unstressed vowels, making the "e" sound much more closed or nearly silent (sounding almost like n'stes).

Brazilian Portuguese Examples

1. Nestes livros, você vai encontrar a resposta. (In these books, you are going to find the answer.)
2. Não confio nestes documentos. (I don't trust these documents.)
3. Nestes dias, o clima está muito quente. (In these days, the weather is very hot.)
4. Coloque os materiais nestes envelopes. (Put the materials in these envelopes.)
5. Nestes casos, o médico recomenda repouso. (In these cases, the doctor recommends rest.)

Continental Portuguese Examples

1. Nestes livros, encontrarás a resposta. (In these books, you will find the answer.)
2. Não confio nestes documentos. (I don't trust these documents.)
3. Nestes dias, o tempo está muito quente. (In these days, the weather is very hot.)
4. Coloca os materiais nestes envelopes. (Put the materials in these envelopes.)
5. Nestes casos, o médico recomenda repouso. (In these cases, the doctor recommends rest.)