Thanks for the UK census info. I have not been able to find a lot of the sons after the 1891 census apart from Clement who stayed in the UK. Just for your amusement, Clement's middle name was Septimus!
My guess is that the missing sons emigrated to somewhere. I have the clue from Ellis Island that Sidney arrived in the US in 1902 en route to meet his brother Lawrence/Laurence in Chicago. That's where the trail stops (for the moment anyway).