Sir i want advice for children custody

Respected sir, im Mohammad Javed unmarried, im in living relationship with already hindu married women for 10 years im taking care of her and her kids boy and girl from boy age 3 and girl 2 years old, now they both kids age was boy 15 and girl 13, Sir i convert they names Hindus to Muslim because i need to admission in school so I gave a muslim name Harsha as Mohammad sami varshini as Sony begum her ex husband married 6 years before with another woman they have two kids with her second wife without divorce first wife.. sir after 18 years old of children is there possible to ask his children back to him I don't want to give my children.