"The two brothers died."
Translation:Les deux frères sont morts.
Mourraient is imperfect, isn't it? Meaning "The two brothers were dying"? Very different.
the imperfect of verb "mourir" is MOURAIENT (only one R)
you are right "les deux frères mouraient" means "were dying"
"the two brothers died" can be translated either with the compound past or with the simple past (isolated action in the past), so:
-- les deux frères sont morts -- les deux frères moururent
- last but not least, "les deux frères mouRRaient" means "the two brothers WOULD die" (past conditional)
Indeed, with the auxiliary "être" and "mort(e)(s)" being either a past participle or an adjective, you can't know whether "ils sont morts" refers to the moment they passed away or to their current status. But of course, context will tell if the difference is important.
"the auxiliary "être"" I'm not sure if it's really a compliment to my French skills or not that catching a typo in French feels so rewarding... :-)