The weight doesn't matter, the thickness determines the length of time you need to cook them.
129 will get you medium-rare.
1 hour likely isn't long enough (unless they're thin steaks).
Sansaire has a good thickness guide here: https://sansaire.com/cook-steak-sous-vide/
Also, how much you're cooking in your bath, shouldn't affect your cooking time. As you're adding several pounds, I'd have the bath up to temperature before adding the meat.