have Eurail pass, no seats available...

When is your trip? Maybe someone knows a trick to getting these reservations.

If not, have you checked the price of advance-purchase tickets on these routes? It might be reasonable to return the Pass ( it is refundable less a service charge of "at least 15%") and just buy tickets. Or look into a Spain pass from Renfe.

Yes, your travel period is key to this question. Without checking, I might have indeed thought it best to reserve only Antequera-Madrid. But if you're actually coming from Granada, then it works better at https://ricksteves.raileurope.com/us/rail/point_to_point/triprequest.htm to reserve from Granada. My test date was May 21. No problem on the same date for the other routes, either. You should also be able to make some reservations at the first train station or travel agency where you get your pass activated, unless you're going to Pamplona for the running of the bulls, in which case that would be too late.

What dates?

Is your pass 1st or 2nd class? If 1st you can check for 2nd class seats.

It seems the Renfe website is not functioning properly right now. Perhaps that is the problem. I cannot find any tickets on the routes I checked, looking now for mid-June and also closer in. That doesn't seem right.

The travel dates are 28 May to 12 June. I did think about returning the pass, and maybe that will be the best thing to do. However, I'm a little anxious about purchasing tickets as we go. The advantage there is that single-trip tickets come with a seat (I think that's right).

Also, forgot to mention- the pass is for second-class seats.

Would you mind posting your exact dates for each trip? Sometimes you can tweak the routing a bit and get what you need.

Are you trying to book on the Renfe site?

Renfe tickets as you go are going to be quite expensive. Part of your dates of travel are after the June scheduled date changes. Renfe can be slow to get these up and running and that might be part of the problem it isn't working well - however others said the new schedule was up as of the past weekend.
The one thing I don't know, however, is whether you book your Eurail pass reservations on the Renfe or another site. If you have the option, check loco2.com as they also sell spain tickets (in English, with seemingly less hassle with credit card glitches).

Thank you, everyone. I will check the loco2.com site. Have not used that before.

You can also try :

https://www.trainline.eu/

they do not charge any booking fees

All is well, I think- had success on the Rail Europe site. Thanks again.

Reason #243 not to buy a rail pass...

People often argue that a pass offers flexibility and spontaneity, however, it does not when you have to reserve seats. If you have to pick a train ahead of time, buy straight from the actual rail carrier at a huge discount. Guaranteed to cost much less than a pass - every time.