was the Assumption of Mary and its perpetual Virginity were copied from Gnostic Apocryphal books ?
Nope. Not at all. In fact, the Gnostics didn't like the idea of physical bodies being resurrected anyway. They would have probably opposed the glorification and assumption of the Theotokos's body.
were the fathers influenced by Gnostics ?
Often times, "gnostic" is wrongly taken to mean "Greek philosophy-influenced". The Fathers certainly were influenced by Platonism and Neo-Platonism and Aristotelianism, etc, all Greek philosophical schools.
Gnosticism, however, refers to movements that allowed non-apostolic use of Greek philosophy to actually overthrow the Gospel and the truths of Christianity. Unlike the author of St. John's Gospel, they did not use hellenistic philosophy to exegete Christ, but rather to oppose him.
The Fathers did "baptise" some Gnostic texts, like the Vision of St. Theodora. How successfully they did so is debatable.