Responses
The think it's more about undertone. If he succeed in killing Carcel, he would then always be near Ines in every possible occasion, then he would try to summon her to the palace for whatever reason and lastly he would spread the rumors about her being his mistress while pretending he's merely jesting to the point everyone believes that she is.
Of course if that scenario happened like you said Ines and her family would not allow it but Oscar is powerful enough for it to be a possibility
Guys, Oscar is not all powerful. He cannot force Ines to be his mistress. If he could’ve compelled Ines to marry him, Ines wouldn’t be married to Carcel but him instead. He can plot all he wants but he cannot force Ines.
First, Ines will not allow herself to be forced by Oscar.
Second, Carcel will not allow his wife to fall into Oscar’s hands
Third, Carcel’s father, who is Oscar’s biggest political supporter, would not allow it. Oscar might think he would but he would not.
Fourth, Ines’s father would never allow it.