Facebook: either permanently deletes or reforms the profile to a memorial page for its users who pass away.
Friends and family in this case will be able to continue posting onto the user’s wall. A user can also choose a ‘legacy contact’ who has limited control of your account once the user passes away.
Twitter: on the other hand, allows an authorized person to act on the deceased’s behalf.
The authorized person will need to provide Twitter with an extensive list of proof, including the user’s death certificate and a copy of ID. Although, the user’s family will not be able to send their final Tweet. They won’t get any access to the user’s account whatsoever, it just gets deactivated.
Instagram: lets the user’s profile be memorialised.
All of the user’s photos will be safe, and like Twitter, no one is allowed access into the user’s account. According to the Mirror: “Posts the deceased person shared stay on Instagram and are visible to the audience they were shared with, but memorialised accounts don’t appear in public spaces like searches.”