An ambiguity of pronoun 'se' you should take into account.
Se is a very powerful word in Portuguese, and may have several meanings according to the context.
For example, the sentence
may have the following meanings:
a) They hurt themselves.
b) They hurt each other.
c) They were hurt.
Many times you can guess the meaning by the context. However sometimes not.
In these cases, you must add a disambiguator, respectively:
a) Eles feriram-se a eles mesmos.
b) Eles feriram-se uns aos outros.
c) Eles feriram-se.