Sometimes the consequence to having obnoxious behaviour is that even the best of kids get fed up and bite you! I wouldn't worry to much stress about him being bitten. Let his parents know exactly why he was bitten. It was a last resort of a fed up child that was being cornered. Obviously you don't want the 18month old to get in the habit of biting all the time but if she has no other means to free herself of a child that is out to bother her then it is better she bites then just sits passively. (is it wrong of me to say this?)

At 23 months when he comes to you after being bitten sooth him but make sure he knows why he was bitten. He should understand it enough and hopefully that is incentive to stop some of the behaviors.

All you can do is put him in isolation (playpen with toys or high chair with toys) when you are busy and shadow him when you can.