I have to make a topsy turvy cake. My first one!  This is for family.  I already know I will be running short on time. I was thinking that possibly I could purchase cakes from the bakery and cover these in fondant.  I know these will not taste as good as what I could make at home but figured everyone will just have to deal with it.  However, I know the cakes we have bought from grocery stores are usually sort of soft.  Do you guys think I should be concerned they wouldn't hold up under the weight of the fondant well?  I may be worrying over nothing but didn't want to plan on this and end up with cakes falling apart.  Thanks for anyone and everyones help.

Hope

Use a good filling and probably no one will notice. Carve while partly frozen and use ganache under the fondant, that will give them the needed stability.

Baking the cakes is one of the quickest parts, and you will still have to make your own frosting to ice them once they are carved. So you will have two types of frosting in there, I would use a box mix over pre-made.

You will also have a hard time finding the right sizes for a topsy turvy, at our stores they usually only have 8" cakes.

Thanks for the input.  I really appreciate it.

Ok, you guys have talked me into it.  I guess I'll make my own ahead of time and freeze.  I usually like mine to be frozen and thawed anyway.  I've just never filled and crumb coated then frozen.  Thanks again for the thoughts on this.

AI would make your own ahead of time, you can keep them frozen for a while! I think peeling off their stuff and carving, plus paying for it will just be a bigger mess.