Still can't work out father-in-law, but it may come to me in the wee small hours.
A friend once told me she can't listen to 'Sweet Thames Flow Softly' without imagining all those foggies creeping on the river. But then she was also puzzled by the line in 'Farewell to Tarwathie'

With our shipbumper full, we will homeward repair

She knew what a bumper on a car was, but...