is this correct french?

Ils passent beaucoup de temps à l'ordinateur (at the computer) / devant l'ordinateur (litrally in front of it. Anyway the previous possibility is better).
Ils ont une vie stressante (you mean stressful)


:)

😉 Bonjour, Hello

Baby Queen is right, it's well :

'' Ils ont une vie stressante ''. However it's better to say : '' Ils passent beaucoup de temps devant l'ordinateur '', instead of say : à l'ordinateur.

~~ Have a nice day ~~

Cat. •That's all

_ *: ･ﾟ✧Je suis / I'm (= I support ) :
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You need a capital to start each sentence.