Hello Indi, You're asking for an action yet finished. Some guys went to a place, and there, they had fun. Then, the answer, the only possible is : Se divirtieron. In English te verb "divertirse" is "to have fun". In English, when you want to express "se divertían" you have a very precise form : they used to have fun.

They had fun = Se diviertieron They were having fun = Se estaban divirtiendo But "Se divertían" can be used in two ways. You can use it to explain that some people was having fun at some point in the past (you can add that they don´t have fun any more). So it´s not a direct translation to "They used to have fun" to which, "Solían divertirse" is a more exact translation. The difference between those two is that "Se divertían" can be used as Josep said as a parallel action to another one and in other cases. "Solían divertirse" is used to express that they were "accustomed" to doing that. So one can imply the continuation of an action over an extended period of time "Solían divertirse" while the other can´t "Se divertían" which can span a moment in time.

to make it clearer, maybe. they were having fun at the party: se divertian en la fiesta; they had fun at the party: se divirtieron en la fiesta. the first you relate what was happening in the party while on it. the second you relate the party is over and the result for those there is that they had fun.

hello, in spanish past uses two moods that english doesn't use. your questions has two answers: a) se divertieron; that when the phrase implyes than the action is finished. (it happened and you tell it as a result). b) se divertian; that when you imply than the action has some continuity or is simulataneous with some other action. here an english would say "they were having fun". Never heard anybody before from st lucia. i'd like to know about. cheers.