Hi there. Your personal insurance won’t cover the Motability car, the only permitted drivers are those on the policy. Your other question is one that pops up often. Yes, it is for the disabled persons benefit, but, say for instance you were using the car to commute to your workplace; this is a benefit to your wife, you are providing income.
No doubt there will be more replies, but the best place for information is Motability, you’ll find them very helpful.