I think the trouble is Jill you kinda came in with the wrong title asking how do I discipline these step grandkids sounding very draconian, most people know you don’t discipline someone else’s children
You also seem to have very set ideas that because you cook good food they should be prepared to eat it that won’t work either as you ve found out kids tastes change and they aren’t all perfect with eating
You say you have a grandchild you adore so that’s great but just because these don’t fit in with your standards don’t make them baddies They sound like fairly normal 5/7 year olds and I presume they are only come for a short visit with their grandad
You haven’t said one nice thing about them in all your posts only the negative I have a feeling that you are a lady who likes control and calm, and for a few days you need to relax and try to ENJOY them, get on the floor and play with them, chat to them talk about their friends, their hobbies, their school, get some garden toys in, some colouring stuff , some puzzles
(charity shops have all sorts cheap as chips) and let them enjoy their little holiday with a grandad who loves them
You can clear up when they ve gone, breath a sigh of relief and get back to your ordered life, but for a few days let your hair down you might even enjoy them
This isn’t meant as a harsh post but realistic