Could be a faulty CL module. Mine only worked with the keys in the doors at first, but the cycling worked. It came with a 'seperate ford fob' but never worked well even after re-pairing. So went down the line of a new genuine 'focus' key fob. Has worked fine ever since. I would be surprised if your van hasn't got remote central locking to be honest. So sounds like a CL module problem. Not an expert on this, just know that what I did worked, as the 'ignition on-off pairing' worked, and went from there. Definitely does sound like a case of worn keys though too!
Good luck pal
K