AHello! I am wanting to make a closed bible cake to feed 12-15 people. Can anyone help with cake size? I was thinking a 2" 9x13 cut in half and stacked but I'm not sure that will work out. Thanks!

When I do closed books...I make them as quarter sheets...my quarters are 8x12.   I have made a quarter sheet book on the bottom, then used half of a quarter and stacked it on top.  You can use any size really that you want.  Bibles come in all sizes.