I am an expert now in this.
In this situation, with credits but no way to use them before they expire: First, combine all credits, PER person, into one credit per person. (book a flight for the amount of the credits combined, or a little more, then cancel it right away, your credits will be combined, and you will get a refund for any overage).
Then you have to wait until the credit expires. You have a year to extend the credit, and you can only extend it once, for 6 months. So time the extension according to when your next trip is scheduled. They take $75 off the credit for this. They email you a LUV credit, which can take a few hours, days, it varies. You can use the LUV vouchers to book online.
I cannot confirm this by experience, but the SW employee I spoke to a week ago (the last time I did an extension) insisted that the LUV credits can be used by someone other than the name on the LUV voucher. Which could be useful, if true.
If anyone has any corrections to this, let me know, this is how I understand it.