Oscar also remembers the first life which everyone had forgotten about.

Where Carcel died on battle field and Ines died because she was poisoned by Alicia. And Oscar was sentenced to death unjustly because of Emiliano's coup.

Then Anastasio reincarnated them with a wish. Oscar wished for his memories to be kept from 1st life while Ines wished to not marry Carcel again because of the guilt that she couldn't bore Carcel's child.

Carcel only had dreams about their past lives and hes confirming his speculations through Emiliano.

Because in their second lives, which they believe is their first, Ines was married to Oscar. While in third, which they believe is their second, Ines ended with Emiliano.

Hence Carcel can't just ask Oscar, he went to Emiliano.

P.s: i think none of them actually remembers their first lives where Ines and Carcel were married. Ines just started having dreams about it too.

As for the rest, Ines, Emiliano and Oscar remember the past two lives and Carcel doesn't.