i come accross this issue

use of perfective when they came and stayed

Когда пришли мои товариши, мы сделали что-то
When my comrades arrived, we did something

then use of imperfective when we want to mean that they came and went back.

Они приходили но никого не было дома
They arrived but nobody was at home

Which tense to use when you want to express continuous past like

While they were arriving, they got shot by a crook.
Когда они приходили, .... ???
Alors qu'ils arrivaient

thx