If you do the level 22, then the 26, you will still get 6 coins total. It'll just be 3 from 22, 3 from 26. If you decide to do the highest difficulty after that, you get another 3 for a max of 9 total. If you do 26 right away, you get the six right away, etc.Well, I'm pretty sure you lose out on the rewards of the higher tiers if you do any of the lower ones. So I can't help, sorry.
22 would make me short one coin.
Edit: beaten.
Good luck.I'll try and do it too, hope it works.