se estaban

were

→ se
phrase Uncommon #21,476
were Used with a gerund to form the past progressive, often with reflexive verbs: se estaban riendo = they were laughing.
SP: Se estaban preparando para salir.
EN: They were getting ready to leave.

Todo el tiempo se estaban disparando.

They were shooting at each other all the time.

— Uno de los nuestros (1990)

Se estaban quemando las yemas de los dedos con lejía.

The tips of their fingers were getting burned by bleach.

— El club de la lucha (1999)

Se estaban riendo de mí.

They were laughing at me.

Los pájaros se estaban comiendo sus pensamientos y recuerdos.

The birds were eating his thoughts and memories.

Ellos se estaban vistiendo.

They were getting dressed.

Ellas se estaban divirtiendo.

They were having fun.

Se estaban poniendo agresivos.

They were becoming aggressive.

— Queen (2014)

Se estaban yendo, cuando nos oyeron.

They were leaving when they heard us.

Sí, los miré cuando se estaban yendo.

Yes, I looked at them when they were leaving.

Dos hombres se estaban peleando en la calle.

Two men were fighting in the street.

No sabía que Tom y Mary se estaban muriendo.

I didn't know Tom and Mary were dying.

Se estaban riendo a carcajadas.

They were laughing their heads off.

Ellos se estaban criticando el uno al otro.

They were criticizing each other.

Se estaban peleando en la calle.

They were fighting in the street.

Se estaban riendo.

They were laughing.

— Blade Runner 2049 (2017)