I think 'the MiL' is entitled to 'cash in' on her own business. She had her own business before her 'royal connection' and she's entitled to promote that business. Has she advertised "The MiL of the PoW presents the new 'Party Pieces' range "Kensington Kiddies"? No. As far as the Rover deal, the headline says 'it's reported' making it a rumour.
I guess I'm American enough to feel that as long as the Middletons don't directly name and use their relationship with Kate and William and as long as they aren't trying to peddle 'influence' with K & W, then they can do what they want with their own names and their own business.
H & M are different. They're making money on the backs of the RF in a nasty way. If H&M had started, oh say, a clothing business that made scads of money I'd say well done to them. If M had restarted her acting career or H had written a smash hit spy novel and both landed major contracts, I say well done to them. But that's not what they've done. They're direct members of the family selling nasty (IMO false or 'spun') stories in order to build up their own 'brand'. They're making their money in a dirty way.