This really is a vexed question. Most of the wives of MPs I know who work for their husbands do a proper day's work and are rewarded accordingly. However, when I worked in the Commons in the mid 1980s there were loads of wives on all sides of the House who did very little if anything. At that time, the salary allowance came to a grand total of £12,000. How times have changed.
When I stood as a candidate in the last election I made ten pledges about how I would conduct myself if I was elected. A fat lot of good it did me, but one of the pledges (and you can look it up, if you don't believe me) was that I would not employ a member of my family. This was done not because I thought it would be wrong to do so, but it was to avoid the perception of any favouritism or wrongdoing. I made this decision for myself, but I do not say that is necessarily right for others. For one thing, I don't have a wife!
Each MP must be open and transparent about their employment arrangements. While publishing the actual salaries of individual staff members would, I feel, be a step too far, every MP should now overtly register any family member who is employed, or receives a pass.