Thank you for your question and pictures for Extension. I'm sorry you lost your 60-year-old tree. I can see you had success in rooting your willow cuttings in water. They are fairly easy to propagate and successfully replant. The critical part will be over-wintering them so you can give to your friends next year. I agree with the method you describe although I would put them in large pots with soil including sphagnum moss, water them well and if you can trench the pots into your garden and cover the pots with burlap would be the best. Put garden soil on top of the plants and it should help in the freeze/thaw cycle of winter and bury your pots as deep as possible. Here is a good article on willow propagation: 

https://shuncy.com/article/how-to-grow-a-willow-tree-from-a-branch

Good luck with your project!

Grass clippings will work as long as they cover the pots.