Will the second half of the batter deflate from the waiting time and produce denser cakes then the first batch? Thanks.

I've not made this particular recipe myself, but I doubt the second half of the batter would suffer much in the waiting time. It's not really a true sponge cake, since it is not relying only on the eggs for the leavening. Self rising flour contains chemical leaveners, and it also calls for baking powder. Both of those will be activated by the heat of the oven, rather than simply by mixing and reacting with an acid. The baking time for the first batch is relatively short as well, so if you have the second batch already loaded into prepared pans - you probably won't notice any difference at all, or minimal at the least.