I am not an express fan.. but what I need to help you is screenshots from your airport utility.
I think it would be smart to
1. Factory reset the Express.. it is lost and if you run Yosemite that is no surprise.
2. If you use iphone or ipad then try using the airport utility in that to do the setup.. it is better than Yosemite.
3. If you do it from computer.. try plugging the express LAN port to the computer.. Leave the TC off.. so there is no Apple wifi to connect to. And turn off the wireless in the computer.. delete all the current wireless names.. then turn wireless back on again.. You want it to be usable by the airport utility but not linked to the resort wifi.
Then start the setup..
Apple do make logical choices based on how you have the express configured.. if it finds itself in this setup it might actually work..
If it does not come up with correct setup then choose from options.
Here is how I did it on airport time capsule..
The utility picks something.. I do not want it to extend.. so click options.
I want to add it to an existing network.
In your case you would add to existing network.. and the option to Join a wireless network should be there.
If you cannot make sense of it I will get Bob Timmons to help as he uses this setup often and knows it very well using the Express.