Oh Clover, that sounds utterly exhausting. Just reading your description I feel overwhelmed. That your children are clothed and fed... you are doing brilliantly. Let alone to be stretching you poor tired brain to manage Christmas and considering dietary changes. I 100% agree with making long-term, consistent changes to diet, but go easy on yourself in establishing it. It'll take time for you to learn what works and for your kids to adjust to the changes. It sounds like you could use way more help though.
I have read bits and pieces of your other threads and I think you're about to/considering a move? Do you know what professional and social supports are available where you're going? You can't do this all on your own. No one can. You are, for now, but you deserve a break, some strategies and a big cuddle.
Here's a virtual one in the meanwhile.