You need to communicate with your W about the kids openly and clearly. You said that you don't even know if she has received the proposal, let alone had time to go over it with a L. It sure seems like keeping the kids away from her until she agrees to something is HIGHLY controlling. If you are worried about the safety of your kids it might be justified, but short of that it seems inappropriate. Why does the L think it is a good idea not to let the kids go with her?
You need to tell her that you would like to talk about a childcare plan, and then explain what you have drawn up. I don't think doing it with a metaphorical gun to her head (not releasing the kids to her) is a fair way to negotiate.
W left me and took the kids. It was wrong of her to take the kids away from their home and with no childcare plan in place. In addition, she has been extremely controlling of where and when I can see the kids, until letting me have them for a couple of weeks.
The childcare plan being proposed is that the kids are with me on school days. School holidays end in a few days so they need to be in a routinue in the next few days. If W doesn't like it then she would have to take me to court which could take months.
However, if W takes the kids away from home and starts the school routine then it puts me a bad position with custody of the kids and it would then be me having to take her to court which could take months.
In addition, the kids are better off being with me on school days because W gets her parents to do nearly all of the childcare for her anyway plus their house doesn't have some basic home comforts that the kids enjoy at home.
It seems that W wants a D and also wants the home to be sold which would mean me having to live outside of the area and so perhaps lose seeing the kids so much.