I'm not an expert on Regencies, however, I've read enough (and have studied history enough) to know that:
a. A child born out of wedlock can never inherit--even if the current heir marries the mother in order to give him a name--he wasn't born in the marital bed=not the rightful heir.
b. In the will of the Marquess that died, he leaves this Park (assuming that to be the whole spread) to Kit's mother (Kathryn, the woman that was presumably his mistress). Also before that, he'd gifted the dowager cottage to her father, then to her. Neither of these things could happen. Why? Because they're entailed, they actually belong to the title, therefore they cannot be sold or gifted.
c. I was under the impression that a person in mourning was not to marry unless extreme circumstances, Ms. Lee says that it's okay, as long as they don't announce. I really couldn't find a right answer on that, so I accepted what she wrote. However, I've only read two books where it happened when only the man was in mourning and he'd impregnated a woman and had to make things right.
For the inconsistency: (Major Spoiler below)
Kit, the little boy, is nearly four, Andrew and Kathryn's marriage was supposed to take place four years ago...how can that be? I know, I know that Kit was given to Kathryn three months after her other son died. However, that would still make him two instead of three, nearly four. She had nine months to carry her first, then he died at 8 months, that's nearly a year and a half. Then three months later, George brought her Christopher, who had to have been a young baby for people to have actually believed she'd just had him...I don't know how nobody would have questioned it otherwise. It's not like three months after burying her first son who was eight months old, she could show up with a child more than a month or two in age and be able to pass him off as hers as well as she did. Plus with her husband having died only six months earlier, that would have branded her an adulteress as well.
Finally, to my way of thinking it was just plain gross to think of sleeping with father and son or from his point of view sleeping with the woman you've always loved while thinking your father had. The ick factor of that made me cringe. Thank goodness we finally find out she did not sleep with both, however until page 268 (out of 309) we're under the impression that she did. And several times Kathryn even says something about it by asking that Andrew if he doesn't mind his father's leavings or making mention she was his father's mistress.
The only way I actually finished this book was because someone ruined the "surprise" for me. Otherwise I wouldn't have made it past page fifty thinking of a woman sleeping with father and son.