What is the fate of the children born as a result of the father marrying two women without their knowledge, and then his children married and had children due to his long absence?

Incestuous marriages are invalid by consensus (ijma'). Verse (An-Nisa: 23) prohibits marriage to mothers, daughters, sisters, paternal aunts, maternal aunts, nieces (daughters of brothers and sisters), foster mothers, foster sisters, mothers-in-law, stepdaughters (daughters of wives), daughters-in-law (wives of sons), and marrying two sisters simultaneously. If such a marriage occurs without the knowledge of both parties, it is considered a 'marriage of شبهة' (doubtful marriage) which precludes the legal punishment (hadd), and the children are attributed to their father.