What should I do about the repeated abuses against the religion, the Prophet (peace be upon him), the Companions, and the Mothers of the Believers on social media, and will I be held accountable for not responding to them?

You must avoid everything that harms the self, and harms Allah and His Messenger, such as posts containing insults and curses, and maintain the soundness of the heart, and avoid places of tribulation. If you come across something like that, and the discussion brings more insults and curses, then avoid it, as Allah Almighty says: "And do not insult those they invoke other than Allah, lest they insult Allah in enmity without knowledge." However, if benefit is hoped for and the misconception can be removed, and you have sufficient knowledge, then write your response with kindness, otherwise do not speak. When debating, let it be with wisdom and good counsel, as Allah Almighty says: "Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best." If you refrain from that due to lack of knowledge or fear of tribulation, there is no sin upon you, for the ways of inviting to Allah and supporting the religion are many.