Mike Makaab, the CEO of Prosport International, which represents both players, was reluctant to comment when asked about the pair's future at Mayfair.
"I cannot comment unless Pirates have made an official statement," Makaab told KickOff.com.
Sikhakhane spent the past campaign on loan at AmaZulu, having joined Pirates from Golden Arrows the season before.
The 25-year-old played 18 league games for Usuthu, but his prospects of game-time at Mayfair have taken strain with Bucs' signing of fellow right-backs Asavela Mbekile and Abel Mabaso.
Van Heerden, who has also turned out for AmaZulu, only played twice in the league in 2017/18, notably scoring with a curling free-kick against Mamelodi Sundowns in November last year.
He played second fiddle to Innocent Maela, who made the left-back position his own following a successful loan spell at the now-defunct Thanda Royal Zulu. Maela will have to compete with another recruit Paseko Mako going forward.
Van Heerden initially linked up with the Buccaneers in the second half of 2016/17 from Chippa United.
Meanwhile, this website understands that Wayne Sandilands is likely to make way to accommodate the capture of ex-Kaizer Chiefs goalkeeper Brilliant Khuzwayo.
Jackson Mabokgwane and Siyabonga Mpontshane are the other keepers at coach Milutin Sredojevic's disposal.