Réponse :

1) We will have to

2) will have to

3) won't be able to ou will not be able to ; will have to ; will have to

4) will have to

Explications :

Rappel sur la possibilité/impossibilité au futur :

Pour l'exprimer, on utilise "Will be able to" + V | Won't be able to ou will not be able to + V concernant la forme négative (=> impossibilité)

Pour l'obligation / non obligation : Will have to + V ; Will not have to + V