Well Bee has to suffer from karma one way. Pim's evil plan contributes to this because Bee's own kids with Khun Luang are getting together without knowing they are brother and sister, and not to mention, older sister and younger brother! Pim wants Bee to "rup and chot chai gum" because Pim blames Bee for her miscarriage.
The pra'ek, on the other hand, I think is both twins because they both belong to Khun Luang and Mali.