I agree with A on what she said. I wanted to add that there seems to be a disconnect for you about how moving someone in will effect everyone. It sounds to me that you are making an assumption that this young woman would want to be taken care of monetarily or at least that this is what you would do because you can afford it. Apart from the fact that she seems to be creating her own success in life and doesn't need your money, this issue of moving in has nothing to do with money or taking the responsibility of money out of someone's hands. This is to do with emotions, creating a healthy home and life for each person involved, including kids.
Read the tags under "moving in." There are very few, if any success stories with the situaion you describe. I personally have responded to many people who have stopped posting here (embarassed, ashamed, don't want to be a downer) that have not had success when rushing partners into their house, or moving them in to take care of them, or expecting a spouse who has been cheated on to accept a new woman at a stage when she is mourning the loss of her relationship as she knew it and feeling the repercussions of betrayal and deception. As far as I have known for the 15 years of being poly and three years of writing here it just is not a good idea. These things take time and process, as I mentioned in my last post.
Why doesn't it work? Well, kids get attached and then are left hurt when they are told "love your other mother (or something of the like)" and then she is gone after a time. This woman might of been an au par, but she and they will see a difference. She is not hired, she is your lover. Big difference. Your wife will likely feel she needs to give up time with you, she might feel second best, that she is not enough, that you are still sneaking around behind her back, that you really don't love her, that she has to consider someone else in her life that is forced on her. The other woman might feel second best, that she has no say in her living situation, that she gets the dregs of your time, that the wife always comes first and both might find that they resent each other causing a big fat elephant of drama in the room every moment of our lives. You have a huge task. I know something of that task and I can tell you, it is mostly about time management, stuffing my own shit because my loves have issues and having very little me time.
I don't envy your situation but I am here to tell you I think you need to be realistic. If you do decide to move her in please let us know how that goes. I love to be wrong about this stuff. Seriously, I love to eat my words when people show me their success and happiness. It makes my day because bottom line is that I like to know people have created successful relationship dynamics.
Anyone want to be friends on Facebook?
Send me your name via PM