Well, I thought about it a bit more and, seeing I am literally one step from researching dragon attacks, I decided that I would have just one more go.
Deciding to go for one more hitter, I replaced Wu Kong with 3/60 Chao.
I brought minor healing potions, axes,bombs and those 5 dragon attacks. I had pretty lucky boards during the minions levels, and I was very, very careful, which somehow meant I ONLY used about 8 minor healing potions for these two stages.
When I reached the level with the three bosses, I first launched Gormek, and then hit Lady Locke with Caedmon and Chao. After that, I used all my axes, bombs and dragon attacks. Lady Locke (aka zombie Helena Bonham Carter as I like to call her) burst into a cloud of dust. I had very bad tiles after that, but I somehow managed to finish Sargasso and Kestrel with two of my heroes still standing!
The score was (obviously) not great, but I got the reward. (Unfortunately, the epic coin only gave me Bane, but you cannot have everything.)
THANK YOU FOR YOUR INVALUABLE ADVICE AND ENCOURAGMENT! I wouldn’t have tried again, had you not advised me to give it a go. THANKS!