OK Vicky,
Lets start with Damage Control.
Water Freezing is bad news, but if you get a couple of gallons of RV anti freeze and pour it down the drains that were used and into the stool, it will keep the traps from freezing and mitigate any issues with the black and gray tanks. If you need to do more cleaning at below freezing temps, yes, you can bring a hose in and wash things. But, when done, be sure to do the last step above with antifreeze to save the traps.
Without knowing what windows you have, I can tell you that many can be tripped to open from the outside without great difficulty. Tell LEO that cutting the screen out of the frame DOES qualify as forced entry just about everywhere. If they removed the top of the reefer vent, then someone small (window sized) was hoping for an easy entry point. I can also tell you that the standard door locks used by most RV builders can easily be picked.
Word of warning. Now that they know that they can get in, they will probably be back.
I wish you luck. Make sure you take too many pictures for the insurance adjusters.
Matt