Securing luggage on Spanish trains

Usually not a problem. Perpignan to Barcelona express trains only make 2 stops along the way, and these are exit only. Barcelona to Madrid express trains have only one intermediate stop at Zaragosa. Madrid to Toledo trains are nonstop.

Your small roller bags may fit in the overhead bins over your seat. Take a look at typical train interiors at this site.
https://www.seat61.com/train-travel-in-spain.htm

On fast trains it’s not common for luggage to be stolen, but it’s not unthinkable. Unlike in some countries with stricter social norms around respect for others’ belongings, here you do need to keep an eye on your stuff. A simple trick is to use a small bike-style chain lock to secure your bag to the rack — not an impenetrable solution, but it discourages opportunistic theft.

I saw another suggestion on the Forum recently. It was to attach two bags to each other, rather than to the rack itself. This also discourages someone from grabbing your bag on the way out the door, as the bag is heavier and more unwieldy than they expected, so they're likely to just move on. The poster suggested using a cable lock (like you would have on your bike), but this seems like an unnecessarily heavy thing to drag around. Other options would include
1. the "belts" people put around their bags https://www.amazon.com/Suitcase-Adjustable-Luggage-Packing-Release/dp/B0999BBRY4/ref=sr_1_14_sspa?crid=GV1EEWNMIE8K&dib=eyJ2IjoiMSJ9.WSlymtR6r1yaLHzwcNX5YWWfbsbZB_hNxmTp3lCqzi9Wp06uFckXbrVTaZDxWQiM5uJqWc2XqwNmNr__fz75UhT0xSSFAoapoZ3xaKxHxayxS8yZYO8xF7L-GsXLBUfNaN19uCuqVVqXmZL5cJ6uMZhoCcc4a5J-evLAXuy_ehbvLz_uVV-85i3ScL-Vi-PXMqUAQRjhG9gB52BmWmUcynQRfgwnpkGa7KqpdGpZygJyapC1g5tZIq1rVthWkC-KOq0O6bnrvvSdPjp4x8CPpPzHnrENkO-dXznQ-kmjeDQ.dYppv9jqYlrkioK8Fpxrh6B-mR1zvbTUoBOsq3o4CF0&dib_tag=se&keywords=luggage%2Bstrap&qid=1757862029&sprefix=luggage%2Bstrap%2Caps%2C179&sr=8-14-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9tdGY&th=1
2. a strap that connects two bags together (but attach them by the side handles so it doesn't just make it easier to take two) https://www.amazon.com/Wisdompro-Adjustable-Attachment-Accessories-Connecting/dp/B0B6PMR8NP/ref=sxin_17_pa_sp_search_thematic_sspa?content-id=amzn1.sym.5a2f80d8-3686-499a-bbaa-70664bd0de70%3Aamzn1.sym.5a2f80d8-3686-499a-bbaa-70664bd0de70&crid=GV1EEWNMIE8K&cv_ct_cx=luggage%2Bstrap&keywords=luggage%2Bstrap&pd_rd_i=B0B6PMR8NP&pd_rd_r=3f106eb5-38f2-4ca1-b2bb-26a5bfe0c6ec&pd_rd_w=uFWyr&pd_rd_wg=4cUOG&pf_rd_p=5a2f80d8-3686-499a-bbaa-70664bd0de70&pf_rd_r=93JHNZ0RNGK7G13T7E24&qid=1757861920&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sprefix=luggage%2Bstrap%2Caps%2C179&sr=1-5-6024b2a3-78e4-4fed-8fed-e1613be3bcce-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&th=1
3. A gear tie, which will have other uses during your trip https://www.amazon.com/Nite-Ize-GT12-31-2R3-Original-Reusable/dp/B09Q6JHC2G/ref=sr_1_5?crid=12CCS8AIFHWX8&dib=eyJ2IjoiMSJ9.oHYhFLiRl2Hfbo0V0_-uRO55ObWcKsV_ULdJVr-C7D3JaE7OhBAd89w7JZbFoaPRdI_3gE_Th6gtlEYsiTTPpW27UK9gStDNigC5m9y3aLTMJIB9qJeyekBGsdWacLLpW9j4mfbX87pHKQZkWT3VM_fthq1PfWaCsPB9LYyvVP5EWIC-2J84OqIgzlNxlJm6O0pwCVCfvZcWyk0PVNmju9lV43D6BewJ_04Wh2dePsAyi9-5yaBQ599RcuNAym6i4Kw45OfOIUmibQmbXQwYFAuDUo6rzzBEKqwg4k4fWBw.oLY_1LmJwWyfCv2N0ROPF9iEbIXxnRGIsarY0dl1quM&dib_tag=se&keywords=nite+ize+gear+tie&qid=1757862115&sprefix=nite+ize+gear+ti%2Caps%2C172&sr=8-54.
4. A Hero Clip https://www.amazon.com/HEROCLIP-Carabiner-Camping-Backpack-Organization/dp/B0913CQWKS/ref=sr_1_1?crid=29KE2MRAJOMCK&dib=eyJ2IjoiMSJ9.wndoR6XZ-M8IoOqP0OGFJAQazHWb3J8rToNEagkeNU_laFtYay-Bwq5ZZUExkg5iLG_4H8V1vvyS0d4y9Ib3lCR9MjycUjqu-bME3LeyREJADumNcw8hiSXe4ujTyCBOG8FVilLCPsltpepRR0X7cLxeipRG8EJFwWkdQfWVI14JicyUNHZcK-D5WoHTQCSO3WLKHT2QuPd5htX35Hhc1bZ5VW3E6QGUSjmWXiyQbiiyAA-RIJAnwH_MlqFmqtcoZXpNYAWOnp6PEiWYnZWsqL5G4SdbhLCXa6bL3y9lDmo.uSIsbMr4b5wMzu7HYGIHPhO7MzTbPilsb4Jt75HMalA&dib_tag=se&keywords=hero%2Bclip%2Blarge&qid=1757862258&sprefix=hero%2Bclip%2Blarge%2Caps%2C183&sr=8-1&th=1
5. something else that you already own

You shouldn't have a problem. Since there are 2 of you traveling together, one of you could stand by the luggage rack just before any stops if you can't see your bags from your seats.

While locks and chains may be if use to some, please don't attach or store your luggage in any way that will impede others from stowing their bags.

for a smaller, pocket-size lock option, try 'Lewis N. Clark Cable Luggage Lock', about $13

I have only taken 2 trains in Spain: Madrid to Sarria and SdeC to Madrid. Both times my wheeled carryon suitcase and backpack fit on the overhead shelf easily.

Other trains at various times in France, my wheeled carryon fit as well.

I wouldn’t worry about it.

I've always been able to store carry-on size luggage above my seat on Renfe intercity/Ave/avlo trains.

We took the train from Leon to Madrid today and also took six other trains in the past month. Carryon size bags and backpacks will easily fit in the overhead bins above your seats, which are larger than the overhead bins on most airplanes. The racks at the ends of the train cars are for larger bags - by which I mean large and medium checked bag size. Do not lock your bags to the luggage racks. While not secure it is highly unlikely that your bag will be stolen. If you are unable to stow your luggage above your seats just stand up and watch over it during the very brief stops along the route.