OK... in front of a computer now. I haven't made ALOT of topsy turvies, but the few I've made have never fallen apart, and with each one, I've learned something that make it easier, and the last time time I took notes.
I also bought Sugarshack's video on topsy turvy cakes after my first two and did pick up some things from it...
First and foremost, good sturdy cake that is half-frozen to cold. I usually only use two layers of cake per tier for mine because, like Tonedna, I don't like mine too tall.
Next thing is to bear in mind that anything less than a 3 inch difference in tier sizes is begging for trouble ( i notice the difference between your top and middle tier was only two inches) If there is not a big enough difference, then there is only a very small ring of cake left after you cut the the hole, and that makes it very vulnerable to falling apart.
My last cake, I made each layer for a tier in graduating sized... bottom tier consisted of an 11" and a 10", top tier, 8" and 7". I noticed this save a lot of cake and gave me a good guide to carve the tapering.
I also use ganache for a crumbcoat. Trust me, once you use this you will never go back to buttercream for carved cakes. When the ganache firms up, it hardend well enough to keep everything in place. And then later when you are putting on your fondant, if it comes out bad and you need to start over, you can just peel off your fondant and there is not buttercream mess - the ganache remains on the cake intact and in shape!
So I cut out foamcore circles the size I want the bottom and top of the tier to be. (I use the cake pans to draw the circles to cut out.) At this point I also use the foamcore I cut for the bottom of the tier as a template to make a circle out of wax, parchment or even computer paper. I'll use that later as my guide to cute the hole on the top of the cake or to draw the circle to cut out.
OK... so now I torte the smaller of the two layers of the cake. I use that very stiff dam of icing on the outer edge and make it wider than if I were torting a regular cake, so that even when I carve, there will still be some dam left. Don't torte the bigger tier yet, just set in on the foamcore you cut to fit it. Next stack the smaller cake on top of the bigger one. Then adhere the foamcore that's the size you want the bottom part to be of top of the small tier with a generous dab of icing or ganache. So now, basically, you have a cake sanwich with foamcore as the "bread". Use the foamcores as your guide to carve the cakes. ( I usually put down a big plastic table cloth from the dollar store to catch all the crumbs, and that makes cleanup so much easier)
Once you are happy with the carving, use toothpick as marker beween the bigger layer and the smaller layer. Now, flip the whole sandwhich so that the smaller part is now the bottom where it is suppoed to be. You can now remove the layer that is at the top, making sure the toothpick is in place so that you can use it to align the cake when you put it back. So when you take of the bigger tier, you can then torte that at an angle to get your slope. Sometimes I flip the wedge over and layer it on to of the steep end to ass even more steepness, sometimes I don't. You can also clean up your slope by carving things into the shape you want them. You can now put the larger layer that is now sloped on top of the smaller one, glueing ii on with ganache. Use your toothpicks as your guide to make sure there are aligned properly. At this point you can decide whether you'll attach the cut of wedge to the slope or not. If you do, you can stick it on with more ganache. Whatever you do, at this point, clean up any rough parts with a smaller knife to get it at just the slope you want it to be.
Then, ganache the whole thing! A little bit of ganache goes a long way and it is waaaaay more easier to put on the cake than buttercream. Use a hot spatula and/or benchscraper to get the ganach as smooth as possible. Once it is all nice and smooth, let it sit for atleast 6 hours to allow the ganache time to firm up and harden.
Repeat all of this with all your tiers.
After that, you can brush the ganached cakes with simple syrup or piping gel and roll out your fondant and cover the cakes. You will notice immediately how much easier it is to have ganache under the fondant rather than buttercream.
When everything is fondanted, let those sit for about 4 hours minimum. Now for all the tiers, except the top one, get the paper circle you had cut out and center it on top of the cakes. I usually use a foodwriter to draw the circle on the fondant, using the paper as a guide. Put the paper aside, and using a smaller knife, cut out the hole, making the depth even with the lowest part of the slope where it meets with the circle. This way, you will be able to slide the top tier into place easier. Its also at this point on the cake where you can insert the knife to cut horizontally to make the platform. So cut out the whole and frost the exposed areas with ganache to seal in the freshness. Insert dowels into what would be the platform or the tier that will be on top. You can now slide in the top tiers. Because you let the fondant sit awhile, it will be firm enough now that you can gently tweak it into place with your cupped palms or with the aid of a fondant smoother, without damaging the fondant.
Once you've done this with all your tiers, pipe a string of frosting at all the bases and brush it smooth to seal the "joints" of each tier. Then drive one or two dowels down through the entire length of the cake. I use two, not too close together so that the cake can't rotate around a single dowel. The hole left by the dowel on top of the cake I usually fill with a plug of fondant.
That's it! You can now decorate as you wish. I also usually let my cakes sit at least overnight before I deliver them, so that everything has time to settle and firm up.
I know this is long, but all these steps have helped me to not have a topry turvy disaster, and I hope you can find it helpful, and that you will end up making one that will totally redeem you for the one that fell apart. And I hope the diva gets to hear about it! How rude, inconsiderate and uncompassionate of her! Sounds like she needs to pay more attention at church!
Above all, remember, you rule the cake, the cake doesn't rule you. And no matter how bad you mess up while trying out things, there is no cake police to come and arrest you and take you away. You will still have the freedom to start over, fix it or try another approach. You are the boss of the cake and you have to show it you are!
Hope this helps! I'll post my tutorial when its done.