Special Questions

Hallo dear teachers,

Please, help me with the following sentences and please tell me if the questions formulated based on the sentences are correct.

E.g. 1) The children are taken care of by his sister.

By whom are the children taken care of?

Or

Who are the children taken care of by?

And

Who are taken care of by his sister?

Or

Who is taken care of by hist sister (which of the options is correct?)

(don't we always put Singular after "who"?)

2) She has given me a nice present.

Whom has she given a nice present? (I guess this is correct, right?)

3) They will be having supper from 7 to 7.30.

How long will they been having dinner?

Or

When will they been having dinner (which option is correct?)

Thanks beforehand

With Best Regards

Nata...