Hasa, born in 2004, joins on a permanent deal and has signed a four-year contract with the club, while the 1999-born Zerbin arrives on a permanent transfer with a three-year deal.
Both moves were confirmed through Frosinone's official channels, with the club completing the paperwork on both signings on the same day as it looks to add depth across midfield and the wide areas ahead of the new Serie A campaign.
Frosinone have also made contact with Milan over a possible loan move for Zeroli, though it remains to be seen how the Rossoneri will respond. Milan could look to include a clause entitling them to 50 per cent of any future sale, given they consider Zeroli one of the academy products they intend to build around long term, though second-tier Padova are also interested in the midfielder.
Zeroli spent last season on loan at Juve Stabia, where persistent injury problems limited him to 13 league appearances, though he impressed when available.
Speaking in recent weeks about his path into football, Zeroli reflected on the unusual circumstances that led to his start in the game.
"I used to do karate, then my parents took my brother Bryan to a trial at Vismara. Since he was a bit nervous and started crying, a scout told me, 'Come on, do a couple of touches too, so he gets distracted.'
"I was five years old and enrolled at the local Ardor football school, so I did the trial and in the end they picked me. Back then the 2005 category didn't exist yet, so I started training with boys a year older than me. There's no point hiding it, my dream is to go back and play for Milan permanently. Milan is my life," he said.
Frosinone's dual approach reflects a summer in which the club have targeted both the permanent market and the loan pool to reshape their squad, with the Napoli pair adding immediate first-team options while the Zeroli pursuit represents a longer-term development bet, should the Serie A side be willing to sanction the move.