I don't think the MC is the father of those two girls it doesn't match, if Laura had an affair with her sister's husband and that husband was the MC, the two of them should have to recognize each other at the moment they met, the same goes for the Luara Sister when she meet the MC, what could it be and that the MC's father was Laura's sister's husband, maybe the MC is brother of those two girls, but it doesn't fit that either because the MC's father was married to some other woman only if he had managed to keep two marriages hidden and separate. The parents of the two girls must be some random character that will only be seen or appear in some flashback.