My employer, who runs a small business employing 5 people in the retail industry, recently married and his new wife will do my job in the business for no wages. Is this a genuine redundancy?
No. A genuine redundancy must be where the position is no longer required. It is not linked to whether someone else is willing to do the job for free (which is illegal except in very limited circumstances such as volunteers).
Also were you consulted about this redundancy prior to it occurring? If not then even if there is a business reason for the redundancy it could be unfair due to lack of consultation procedure. This will depend on your industry.
I would say you have been unfairly dismissed and you should make a claim. You have 21 days from the date of the dismissal to do so.