Employing your spouse or child isn't against parliamentary rules - unless they receive taxpayers' money in return for doing nothing, as Derek Conway has discovered.
Employing family members is fairly common among "honourable members" although most would surely employ staff capable of remembering the name of their Dad's constituency secretary. (Something young Freddie Conway was incapable of doing).
Conway took Ted Heath's old seat of Old Bexley and Sidcup but in a previous incarnation was MP for Shrewsbury - and for three years parliamentary private secretary to Wyn Roberts when he was Minister of State at the Welsh Office.
MPs do not have to declare employment of family members in any parliamentary register so it is impossible to discover how widespread the practice is.
It's far easier in Cardiff Bay, where the rules on declaraion appear to be stricter. The last time I checked the register of AMs' interests no fewer than a quarter of Assembly Members did or had employed members of their families.