Duckworth, an outside back, joined the Hawks from Leeds in 2015, and scored three tries in 15 appearances.
“James is very popular amongst the squad and he is a very strong returner of the ball and a good finisher,” said Hunlset director of rugby Darren Williams.
“He is without doubt a top championship performer and to retain his services in league 1 is a real coup for the club.”
Mackay, 25, has signed a one-year contract extension. He joined the Hawks in 2013 from Featherstone Rovers.
“Liam is well respected amongst his own team mates and it was key that we retained his services for 2016,” added Williams.
“His performances in the championship were outstanding and his work rate is second to none. He regularly tops the stats and his retention for 2016 was a priority for the club.”