If you're going to simmer your chili for a long time, just throw it in there. If you made stock with it, you'd still be just simmering the bone for a long time to extract the same flavors. (I'm not advocating not using stock here, just that I wouldn't make stock for the sole purpose of getting flavor out of the bone. Use the stock you would otherwise.).
Simmer four plus hours and then pull the bone out, tap the meat off, and enjoy the chili (although I like to cool chili down, put it in the fridge, and eat it the next day better).
If you're going to make the stock with it though, @Cos definitely has the right idea with the pressure cooker.
Breast of lamb (or veal) is what would be called the belly on a pig -- it's the relatively thin and flat layer of muscle and fat surrounding the ribcage. As such, the bones that you have are in fact ribs, and they're quite easy to remove from the remainder of the meat. Because of the muscle that's between the bones, connecting them, they can be treated as their own layer. All you have to do is free that whole layer from the layer that is just meat. Really, this sounds more complicated than it is.
Lay the breast flat on a board, with the bones on top, ends towards you. Use your boning/filet knife, narrow-bladed slicer, or even a paring knife.
To set yourself up for the cut you'll use for the majority of this process, you need to get the first bone (the one on the side opposite your knife hand) free. With the knife held vertically, cut along the outer edge of that bone, trying to not go deeper than the bone. Just disconnect that side from the meat.
Now, holding the blade parallel to the board, get right under the end of the bone with the tip of the knife. Make a small cut across the breadth of the bone. Ideally the face of the blade should be making contact with the underside of the bone as you cut -- not cutting into the bone, but taking as much meat as possible. Don't sweat it, though: whatever's left attached to the ribs will make a very nice stock.
Make small but smooth cuts further in along the bone, digging out a little slit underneath it. Once you're two or three inches in, move to the next bone in line, and separate it in the same way. You've now got a corner that you can lift up to make it easier to get your knife in there.
Go back to the first bone, and pull up on that corner. Now make your cuts diagonal to the lines of the bones, so that you're separating the first bone further along than the second. Keep the blade parallel to the board, and don't try to do too much at once -- go long but not deep, slicing lightly along the whole underside crease right where the bone and meat are connected, to a quarter inch or so depth. Readjust your grip on the top half, and make another cut.
(If you have a big enough board and table, you might find it easier to turn the breast so the corner you're working from is pointed towards you at this point.)
Repeat that cut all the way across the breast, and keep using your free hand to lift the top part away as you cut. This obviously gives you a better view, but it also actually assists the separation. The meat and the bones are less well-connected to each other than the meat is to itself -- when you put the join under tension, it wants to come apart.
Depending on the size of your slab, once you've got more than a few bones free, constantly lifting the top half may start to be cumbersome. At that point, you can completely separate some of those bones and set them aside -- just cut vertically along the meat between two of them.
That's all there is to it. Turn those ribs into something tasty, too!
Best Answer
Sardines are canned, which means the high heat of a pressure canner. That is what softens the bones. If you are wanting softer bones for other kinds of fish, you can either cook them using a pressure cooker or can them. However, this will only work for smaller fish that have smaller bones.
If your main concern is that you will swallow a bone and choke, then buy your fish as fillets only. Most fish fillets have no bones at all. The pin bones that are in salmon fillets can be removed with needle nose pliers, and are so small that you couldn't choke on them if you tried.