Well as far as I know siamese algae eaters get extremely aggressive and do not make good tankmates for discus.
As for the otos.. I have always kept otos with discus with no problems, but there are others here who have had nothing but trouble with the little guys. And the same goes for bristlenose plecos. Some keep them with no problems and others find they attach to their discus.
IMO it depends on each particular fish and how much they are fed. If you keep your otos or your bristlenose well fed (IE.. vegetables, algae wafers and such supplemented now and again) then you will not have trouble with them attaching to your discus.
HTH!
Amber