Yes, agreed. I wonder whether such a sentence was possible at some point in the past, but with the gradual replacement of subjunctive with indicative, has come to sound ungrammatical.
That's not possible. Mrs Gibbs isn't even there. We know she's at choir practice so Mr Gibbs can't be addressing her as "you". Mr Gibbs has already referred to it being 8.30 and said he's surprised Mrs Gibbs is "out so late". George is young enough to still get an allowance and to say "Yes, pa" when told to do something so it's entirely reasonable to assume that 8.30 is an acceptable bedtime for him.