It is HARD to leave a truly anonymous report because of caller ID and reverse phone directories. The SW cannot tell you who called, but has or can easily get the info on the person who reported.
Dirty dishes? If that were criminal they would not only have taken my kids but put me in prison for life. Mine are only all clean for an hour or so after I get them all done. It is annoying!
The animal issue is because many diseases can travel from human to animal and vice versa. If the animal has something truly contagious to humans, it could be unsafe to have the kids around the animal with-o precautions. So that is why the SW needs to call animal control. They also check because many, if not most very abusive people are also abusive to their pets, so if animal control is worried, they could do a deeper check on you. Of course it is not an issue for you!
File that complaint BEFORE the IEP. Let them know that you won't tolerate the bullying. As for moving Difficult Child, if she is doing better where she is rather than at her home school, but she still needs improvement, it makes no sense to send her back to where she did worse. That truly is violating her FAPE rights.
Have you read through the SPED forum archives for help with IEPs? There is a LOT of info there!