Can't stand my SIL's kids?

They are nightmares. Her 4yo tattles constantly, pees her pants every hour on the hour, and is so destructive! And when you try to explain to her that she shouldn't do something or that she does something wrong, rather than acknowledging you or saying "I'm sorry" she hides on a corner and screams for her mom. She's started a new game where she will antagonize my 3yo daughter until she gets mad enough to act out, and then cries like it was my daughter's fault (mine knows better than to hit or bite but she has her limits too). She can't form full sentences yet so trying to get her to say what she wants or what's wrong is a constant challenge. Plus my SIL's 2yo throws an all-out fit when you aren't giving him attention, to the point where he's gotten so red and wouldn't take a breath between cries and we thought he might pass out.

My SIL recently got divorced and moved in with her parents so they are now her live-in babysitters according to her. She's never home and when she is she doesn't pay any attention to the kids. Her mom and I are usually the ones cleaning up after them, changing them, taking care of them, etc. Even her parents have called her out on it. My child is no saint and I'm not a perfect parent by any means... we fight our own battles but it's gotten to the point where I will avoid being around the three of them at all costs and don't like my daughter being around them too often out of fear of picking up their bad habits. What the heck can I do to cope?!