Chara will be seeing their birth parents - as they did love them, once upon a time - and Asriel Dreemurr. Chara will know that all of them are not real, as they died a long time ago and are personally responsible for killing Asriel themselves (yay post-Genocide fun times!). However Chara will also be extremely unhappy to see any of them! Thanks Gods.
It's up in the air who will be killing them, however Asriel's ghost will be lasting longer than Chara's birth parents if things are left to their own devices and will be the ghost that becomes visible to others on the 26th. Anyone is free to take out any of them or let Chara finish the job themselves. As a heads up, however, interacting with Chara and their birth parents will contain themes of child abuse and suicidal thoughts. So if you wish to avoid those subjects it may be best to stick with Asriel's ghost.
no subject
It's up in the air who will be killing them, however Asriel's ghost will be lasting longer than Chara's birth parents if things are left to their own devices and will be the ghost that becomes visible to others on the 26th. Anyone is free to take out any of them or let Chara finish the job themselves. As a heads up, however, interacting with Chara and their birth parents will contain themes of child abuse and suicidal thoughts. So if you wish to avoid those subjects it may be best to stick with Asriel's ghost.