Just on the teeth brushing, he really needs someone to do it for him once a day. Kids don't have the manual dexterity to clean their teeth properly until at least 8. I know they hate having someone do it for them but it does need to happen. I would suggest telling him that he can have a turn after mummy's turn, and maybe singing a song while you're brushing.

A build up of plaque (which contains yucky bacteria) could certainly be contributing to smelly breath/saliva. You might find that after a couple of weeks of really good toothbrushing that the smell improves . HTHs.