It beggars belief that some of them so vociferously try to defend the indefensible. This is nepotism, pure and simple, and another way of extracting public monies. And the analogy often drawn between MPs and a small, family run business is poor - The business is paying for the family members salary out of the turnover the company derives from its sales or services, so no burden on the public purse.
And as a taxpayer, I would like to know that researchers, PAs and secretarial staff are selected for their ability to do the job in question - not because they are living with or are family members of the MP.