The travel office should be able to cut you a ticket from CA to Corpus if the price is equivalent to Fairchild to Corpus. If not, you may have to get your own round trip tickets from Fairchild to California, then resume your official travel from Fairchild to Corpus. This is a pain in the ass, but depending on your travel office, this may be how you have to do it.
N/A when combined with TDY. This statement stems from the fact that you are required to be on leave status, even if you leave or return on a weekend. So if you leave Friday after work and return nine days later on Sunday, all those weekend days are included in your leave because it begins when you are in the local area and does not end until you return. Even if you don't put in for leave, finance will automatically deduct it from your leave balance when you file your voucher that lists the days of leave between your official travel.
As Brabus mentioned, it's not a question for finance, it's a question for the travel office since they're cutting the tickets.