+1 to both of ABQMom's points. Your son is getting extra attention for bad behavior... what kind of attention? Because it's all too possible that you're inadvertently rewarding bad behavior. That's clearly the impression your daughter is getting. If he's tethered to you, it should not be fun for him.
The other plus is about non-intervention, because it seems by now your DD has figured out she can get DS in trouble simply by crying, leaving you to try to figure out what's legit and what isn't.
As for your DH... be patient. Remember, his picture of what goes on is very different from yours, not only because of a different perspective, but also because the whole dynamic changes just because he's there.
For instance, just last night I started getting exasperated with my DD over her apparent neglect of the dog, because I'd seen a pattern all weekend of having to remind her to feed him. DW quickly pointed out that DD has been automatic on it every morning, letting him loose from his crate, taking him outside to potty, and then feeding him without being asked. When I'm home I get up first, so I let the dog loose, take him outside, and throw off her entire routine. The pattern DW sees and the pattern I saw were two very different patterns.
