@Windy Lots of issues in there!
Firstly, when you refer to your wife having a lifetime award, that refers to the benefit, not entitlement to Motability. Whilst the benefit is a gateway to a Motability car, Motability are at liberty to refuse admission (or renewal).
Frequent early lease surrenders add to the costs of the scheme for everyone, so it’s right that they draw the line at some point. If your wife’s condition changes and that makes the car unsuitable then that shouldn’t count against you but, with respect, it sounds as though you may have made some hasty decisions and also not properly considered that the cars meet your current and future needs. My wife also has MS and is a full time wheelchair user. I wouldn’t have even looked at van type vehicles as I would have known that they were too high. I would also know that a Mini would never be suitable as it’s too small, both for us and the wheelchair. If the Peugeot van was meant to have air con but it didn’t then you should have refused to take delivery of it. Maybe the model you ordered didn’t have it as standard and you hadn’t established that before ordering?
You don’t need power of attorney to be able to speak to Motability on your wife’s behalf. I am the sole driver and we agreed with Motability that I am authorised to deal with them – as I do.
I am genuinely sorry to hear about your wife’s issues and your health challenges and I sincerely hope that things work out for you, but I think that the lessons for others here are more about doing your homework when it comes to standard equipment (models in showrooms always have extra cost options fitted), not accepting a car that isn’t exactly what you ordered, ensuring that a car that you choose meets your current and anticipated needs (over the next 3 years) and being aware that whilst Motability are very good at allowing terminations for genuine reasons, they will at some point draw the line.