Hi, the brisket sounds yummy, but hey, if they won't eat it then other ideas are required.
You could drain off the yummy gravy and save it, put the brisket in the food processor and chop it into bits, then turn it into cottage pie - fry the chopped beef with some onions and garlic if liked. Add some chopped, cooked carrots and then stir in the saved gravy. Let it cool and then top with mashed potato. Bake until nice and brown on top.
OR - meatloaf - drain off the gravy and keep for later. Mince/chop the leftover beef in the processor. Add 1 or 2 chopped, cooked onions according to taste, minced garlic if liked, some mustard (any kind), some horseradish, some ketchup, one egg and about 4 slices of bread, made into breadcrumbs. Blitz it all in the processor for a minute or so, then scrape it into a lined baking tin. Cook for about 30/40 mins at 190 C. Turn out, slice and serve with whatever you like, plus the reheated gravy.
2 kilos will do both of the above, which are dead easy to freeze raw.
If you don't fancy the above, you could chop the remainder of the brisket into bits and freeze for making into a casserole/curry/pie?