Sounds like an issue with the door locking mechanisms / actuators. The easiest thing to do first which wouldn't involve the need to dismantle anything would be to get a diagnostics scan on the car to see if there are any electrical faults with the actuators.
Failing that, a visual inspection of the locking mechanisms would be your next port of call for any obvious mechanical issues such as a disconnected or problematic operating cable / rod. To do that you would need to remove the door cards.
Just be aware that removing the front door cards is a bit of a PITA because for some stupid reason SEAT decided to mount the window raising mechanism to the door card itself instead of the door so you have to disconnect and securely suspend the window glass during the card removal process. Instructions for both front and rear door card removal can be found in
this post. Note that there are two links at the top of the post to PDF documents with all the instructions in. The rest of the text in the post describes other things to be aware of during the card removal process that aren't documented in the PDFs.