is the landlord supposed to put us up in a hotel or something ?

Not generally - but read your agreement as you may be entitled to some compensation. Even if its silent, you can always ask.

Your rights regarding situations like this vary by state - more information is available here:

https://www.hud.gov/topics/rental_assistance/tenantrights

Depends on where you live and it would have been on the lease you signed

Depends on what your lease says

I would be surprised if they had to find alternative facilities to use. At least they haven't evacuated the building which woiuld have been more inconvenient.

No.