What are my first few steps to break/help this cycle?

My wife and step daughter seem to be intertwined in a reciprocating cycle, which I would love to help them out of. Wife (W) (age>32), Step Daughter (S/D)(age8). My Son (S) (age 12), My Daughter (D) (age 10)
-Some kind of grief cycle due to late husband(W)/father (S/D) death by suicide 5 years ago.
-S/D pretends to be sick/tired/happy/sad to manipulate W. W always falls for it. (Did I mention that she has Law degree and dual Bachelor’s Degrees)
-S/D manipulates W into helping/doing S/D’s chores, While W encourages S and D to be independent and to do chores on their own.
-S/D pretends to be sick to stay home from school and then is miraculously better and goes to McDonald’s for lunch with W, W doesn’t think twice or notice, but makes my S and D go to school if they are running a fever with no other major symptoms!!
-W appears to NEED to be manipulated by S/D, because no amount of discussion changes or diminishes the manipulation.
-S/D acts like a normal 8 year old girl around me, because I see right through her manipulation, and will not hesitate to apply fair discipline as required to all children.

This isn’t any kind of emergency, but I would like to help somehow besides watching nothing change. These behaviors seem to be on a slow downward spiral, characterized by a weariness for W because so much emotional and physical energy is required by S/D. I usually get the brunt of this imbalance expressed in a lack of patience towards me.

So far I have been journaling to express, digest and work through this and I feel like this experience is developing me as a listener and a person. Still I feel like I am helplessly watching the future life of my S/D and the happiness of my W slowly spiral down the drain.

I have much more thinking out loud to do on this topic, but W isn’t open to my thinking out loud lately, because so much painful truth blunders out of my mind into open space.

Thanks in advance for the paradigm shifting insight flutherers!