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I don't know if you're doing square or round. If it helps with proportions, I do a 3 egg mix in a 10 inch square tin (twice) or split the same quantity bewtween two standard Victoria sandwich tins. So assuming your cakes are roughly the same size as mine, I'd be using a total of 10 eggs.
(I weigh the eggs then use the exact same weight of flour, butter and sugar)
That's what I use to do those sizes of cakes. It will give you cakes that are about 3.5 - 4" tall in total once they're filled and iced.
You will have to trim the tops a little in order to make the cakes perfectly level so they look good once they're stacked - my advice would be to trim them, then turn the top layer of each cake upside down so the trimmed section is in the middle. It will give you a much neater finish when you ice them.