I crack all the same ones as you, along with both ankles (my 2nd favorite crack, so deep and powerful!) and I can only get my left shoulder occasionally (like twice a year by accident, I can't do anything to make it happen), but I have SUCH a hard time getting my back to crack! My sister is the only one who can do it, and she puts so much force into it that she's nearly hurt herself on several occasions. Even chiropractors can't get the same multiple, deep cracks in ONE spot that my sister can - it's truly like 6 cracks. I do the regular laying-on-the-floor and she pushes up and down my spine, and nothing happens. Then at about the bra strap area of my spine, she uses all her weight into the push - thrusts down and then wiggles it up and down a bit without lifting up. Seriously, 6 cracks that change my mood and comfort for days. Chiropractors will get a few tiny cracks from my back because they just won't put in the same amount of force that my sister will. I've had several chiros say that the little cracks are just as important as the big cracks - sorry, I don't buy that.
Anyway, welcome to the forum! I'd love to hear how you get your back to crack - I'm always trying to figure out a way to do it myself!