Sullivan splashed out £574,000 to increase his stake to 24.45% and the Golds between them have spent an additional £895,000 to increase their holding to 25.06%.
David Gold has also individually purchased an additional number of shares for £43,696.
It is another blow to the club's largest individual shareholder Carson Yeung who has attempted to have ex-Liverpool star Steve McManaman and former Crystal Palace player Fan Zhiyi voted onto the board as his representatives.
Yeung was hoping the duo would be voted on at an EGM but the club's managing director Karren Brady recommended shareholders vote against the move in a letter.
Sullivan and David Gold are determined that Yeung will have no extra involvement and will continue to block any moves he makes in that direction.
The debacle over his collapsed takeover bid left them angry and frustrated and also contributed to the departure of the then manager Steve Bruce.