[Grammar] In which house does he live?

[koolade3]

S1. At whom is he laughing?
S2. In which house does he live?
S3. Which house does he live in?


I saw S1 is grammatically incorrect.

But somehow I think S2 can be correct.

S2 can be quite the same as S3.

Is S2 grammatically correct?

 

[Raymott]

S1. At whom is he laughing?
S2. In which house does he live?
S3. Which house does he live in?


I saw S1 is grammatically incorrect.

But somehow I think S2 can be correct.

S2 can be quite the same as S3.

Is S2 grammatically correct?

Yes, they're all correct.
1. would normally be expressed as "Who is he laughing at?"