"You are in the house with the father."
Translation:Du bist mit dem Vater im Haus.
Why shouldn't you have two dative objects? 'in' is a two way preposition. In combination with 'sein', the dative is required.
Dative is when the noun is after a preposition, so "das" changes to "dem", and "in the house" is translated as "in dem Haus" = "im Haus" (in+dem= im). That's my opinion! PD: I hope you excuse me for my English, I'm not a native speaker :$. Grüße!
bei dem vater is totally different Bei is used when you are staying at someone's place ich habe bei meinem Onkel geschlafen , oder zum beispiel gestern war ich bei meinem Freund ...USW don't hesitate to ask if anything is not clear
I believe it should be ( Zu hause ) , I have reached the B1 Stuffe in Goethe Institut and that's how we learned it and that's how I see it anywhere in books and novels