Armstrong, 20 is a defensive midfielder who was player of the year for Braves last season with ten goals and 19 assists. He was on Celtic’s books as a youth before spending three years in New Jersey on a football scholarship.
Swann, 24, is a left-back or left midfielder who came through the ranks at the Fife club and has had loan spells at Whitehill Welfare and Linlithgow Rose.
Brown is an experienced striker who spent the first half of last season at Spartans on loan from East Fife, scoring five goals in seven starts and two substitute appearances for Dougie Samuel’s men before before heading to Bonnyrigg Ross on loan in January to help guide them to SPFL 2 with a play-off goal against Cowdenbeath.
Spartans, who finished fifth last season, have already recruited centre-back Jordan Tapping, 25, from Stenhousemuir, 32-year-old midfielder Gavin Morrison from Cowdenbeath and 21-year-old striker Jamie Penker from Stirling University.
Striker Cameron Dawson, who spent last season on loan at Penicuik Athletic, has been made available for transfer.
The north Edinburgh side have friendlies at home to East Fife on June 25; Threave Rovers on July 2; Hearts XI on July 6; an away game at Musselburgh Athletic on July 12; and a home match against Brechin City on July 16 to prepare for the new campaign.