According to Brahm Puran, Hlad was Hiranyaashipu's son; Sund was Hlad's son and Tadka married Sund. Sund and Tadka gave birth to Mareech.
Hiranyakasipu
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Hlad
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Sund
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Mareech
If you read stories in scriptures in detail, then you will find that looking one way, there was one relation between two people and looking another way, entirely different relation existed between the same two people.