This is a quite interesting topic, where there is no consensus among the masters of traditional BaZi. I do not know what methodology the mangpai school uses in this case. But from my experience, the method when in the chart of the second child the day pillar is replaced by the pillar of the following day showed the best results in explaining the events of the life of twins.

So for example in your case the chart of the first girl stays the same:
    H    D        M        Y
  Ren   Xin    Bing    Wu
 Chen  Chou Chen   Chen

And the chart of the second kid will be
    H     D        M        Y
  Ren   Ren    Bing    Wu
 Chen Yin    Chen   Chen