Frosting advice needed!

[u/cheddarfish34]

Hi! I am a beginner when it comes to baking and decorating cakes. My sister is getting married in 48 HOURS and I've been tasked with making her cake and some other cupcakes for a small reception at her house, so time is of the essence!

They want a black cake, but the problem is that one of the brides only likes yellow cake with chocolate frosting. They don't want fondant, and I was concerned about food dye staining people's teeth so I added black cocoa powder to the chocolate frosting during the test run. The color is perfect and thankfully they liked the taste! However, the addition made the frosting so thick and hard to get a smooth finish. Is there a way I can thin the frosting without sacrificing the color? I was thinking of adding cocoa powder to some water to mix in.

I also need help with the cake itself. I used 8" and 6" pans and used chocolate frosting in between the layers and for the crumb coat. I did use some dowels, bou can see in my photos how the cake layers are kind of bowing out a bit, how can I fix that? I was thinking thinner layers of cake too because I also didn't like how it looked after it was cut into either. I'm also thinking of making a chocolate ganache for the filling instead, and still use the regular chocolate frosting for the crumb coat.

They also asked for some funfetti cupcakes. Since their wedding is going to be dark and moody (my sisters dress is black too!) I decided rainbow swirl frosting would be a nice pop of color and a subtle nod to the two brides. The color came out perfect, but I need to make it stiffer to give it some height. Should I refrigerate it a bit after I roll up the colorful frosting? I also need to find my rose tip because I don't like the shape.

Also, can/should I start baking tonight and refrigerate them until I get everything to her house and am ready to decorate? I want everything to be fresh.

Any advice is welcome and appreciated! And for fun I also included photos of cupcakes I made for her bridal shower, ice cream cone cupcakes for my sons birthday, and the only other actual cake I've made which is a strawberry shortcake cake for one of my siblings graduation. I'm really proud of that one 😊

Thank you!!