I tried my first double barrel cake this past weekend.  It survived but after I added the buttercream decorations I was scared it would crash before the party.  

1.  Do torted layers hold up better than non-torted?  Mine were not torted.

2.  I did not put support between the bottom two cake layers and the top two.  I know that is a problem and will do that from now on.  Will the solve sagging and toppling?

3.  I wonder if my cake is not dense enough to hold up to this cake.  I used Super Moist cake mix.  Is that a problem?

4.  I see tutorials that show these beautiful 2 inch layers that people get.  Mind are coming out much shorter than that but if I put more batter in the pan the cake is not cooked in the middle before the edges dry out.

Any advice or help is so appreciated.  Thanks in advance!

Torted vs not is a personal preference, I like to torte just because Ilike the cake to icing ratio, and it is visually more appealing to me lol when I do double barrel cakes, I always dowel the bottom layer to support the top, so that should solve the sagging problem. What temp are you baking your cakes? I fill my pans more than halfway, bake at 325. I end up with a very small bump at the top, but I cut it off and eat it. Your cake doesn't have to be dense enough, you just have to have the right support in order to support the weight. 

Thank you so much!  Very helpful response!

You're welcome! Hope it helps a little

Sounds like you actually did a 2 tiered cake w/each one a dbl barrel.  If so, then definately dowel the lower tier.  The kind of cake used makes little to no difference - it's the support system that holds the top tiers up,  preventing sagging.  I have made 1,000s of Betty Crocker Super Moist cakes - some of them as large as 5 tiers w/o a problem :)

Thank you!  I always get great reviews on the taste of the BC Super Moist so I'm glad I don't have to abandon it.

Quality control is what I tell my husband 

Right!!!!! You have to make sure the taste is just right!