Firstly get some comfortis, either from your local vet or from here, it's cheaper on the website, but that will rid you of your flea problem within 4 hours and secondly I think you may have to chat to the owners, just keep it friendly and nothing serious but explain that it's a bit of a PITA regarding fleas and urine stentches and they are keeping ppl in your household awake which doesn't help when ds is unwell.

Hope your DS feels better soon and the owners understand