They must not be at home.
Is this the correct way to say "They must not be at home." in Spanish? "No deben de estar en casa."
2 Answers
Yes, you can say "No deben estar en casa" or "Probablemente no esten en casa"
I assume you're using "must" as a modal, right? If so, the translation would be the one proposed by MarimarMty.
If you could provide context, translation will be more accurate!